combinatorics/permutations: Use floor division
combinatorics/permutations: Use floor division

Some code was using the ambiguous division operator on integers. This
produces floats by default in Python 3 (1.0 as opposed to 1) which
cannot be used as list indices. Fix by using floor division (//) where
appropriate. A doctest was also failing, it expected an implicit cast to
int (1.0 to 1 automatically).

Also remove some redundant casts to int, factorial() returns an int
always.

MechCoder/sympy,AkademieOlympia/sympy,atsao72/sympy,Arafatk/sympy,abloomston/sympy,ChristinaZografou/sympy,asm666/sympy,farhaanbukhsh/sympy,kaushik94/sympy,beni55/sympy,atsao72/sympy,MechCoder/sympy,yukoba/sympy,rahuldan/sympy,dqnykamp/sympy,cccfran/sympy,pandeyadarsh/sympy,mafiya69/sympy,ga7g08/sympy,chaffra/sympy,abloomston/sympy,lindsayad/sympy,bukzor/sympy,cswiercz/sympy,pandeyadarsh/sympy,garvitr/sympy,postvakje/sympy,hargup/sympy,liangjiaxing/sympy,kumarkrishna/sympy,Sumith1896/sympy,mcdaniel67/sympy,skidzo/sympy,ga7g08/sympy,rahuldan/sympy,iamutkarshtiwari/sympy,shikil/sympy,yashsharan/sympy,VaibhavAgarwalVA/sympy,hrashk/sympy,jbbskinny/sympy,cswiercz/sympy,aktech/sympy,meghana1995/sympy,postvakje/sympy,MridulS/sympy,vipulroxx/sympy,ahhda/sympy,emon10005/sympy,meghana1995/sympy,pbrady/sympy,sahmed95/sympy,Shaswat27/sympy,wyom/sympy,madan96/sympy,bukzor/sympy,maniteja123/sympy,wanglongqi/sympy,Arafatk/sympy,jbbskinny/sympy,kumarkrishna/sympy,AunShiLord/sympy,kmacinnis/sympy,Designist/sympy,liangjiaxing/sympy,kaichogami/sympy,AkademieOlympia/sympy,sampadsaha5/sympy,mafiya69/sympy,Gadal/sympy,Davidjohnwilson/sympy,meghana1995/sympy,beni55/sympy,sahilshekhawat/sympy,yukoba/sympy,garvitr/sympy,yashsharan/sympy,ga7g08/sympy,Mitchkoens/sympy,lindsayad/sympy,amitjamadagni/sympy,iamutkarshtiwari/sympy,VaibhavAgarwalVA/sympy,Vishluck/sympy,vipulroxx/sympy,diofant/diofant,sampadsaha5/sympy,shikil/sympy,lidavidm/sympy,oliverlee/sympy,MechCoder/sympy,abhiii5459/sympy,jerli/sympy,kevalds51/sympy,yashsharan/sympy,kevalds51/sympy,jerli/sympy,emon10005/sympy,wanglongqi/sympy,Titan-C/sympy,ChristinaZografou/sympy,toolforger/sympy,maniteja123/sympy,sunny94/temp,Designist/sympy,cccfran/sympy,sahilshekhawat/sympy,atreyv/sympy,saurabhjn76/sympy,Shaswat27/sympy,souravsingh/sympy,wanglongqi/sympy,liangjiaxing/sympy,AkademieOlympia/sympy,debugger22/sympy,grevutiu-gabriel/sympy,kmacinnis/sympy,kaichogami/sympy,pandeyadarsh/sympy,atreyv/sympy,mafiya69/sympy,chaffra/sympy,madan96/sympy,toolforger/sympy,lindsayad/sympy,Davidjohnwilson/sympy,sunny94/temp,shikil/sympy,pbrady/sympy,wyom/sympy,souravsingh/sympy,lidavidm/sympy,Designist/sympy,jamesblunt/sympy,Mitchkoens/sympy,skidzo/sympy,mcdaniel67/sympy,oliverlee/sympy,abhiii5459/sympy,Curious72/sympy,VaibhavAgarwalVA/sympy,shipci/sympy,jaimahajan1997/sympy,hargup/sympy,jaimahajan1997/sympy,hrashk/sympy,wyom/sympy,chaffra/sympy,Titan-C/sympy,cswiercz/sympy,jbbskinny/sympy,drufat/sympy,skidzo/sympy,skirpichev/omg,moble/sympy,Vishluck/sympy,hargup/sympy,toolforger/sympy,sahmed95/sympy,Sumith1896/sympy,sahmed95/sympy,moble/sympy,emon10005/sympy,atreyv/sympy,shipci/sympy,kumarkrishna/sympy,farhaanbukhsh/sympy,hrashk/sympy,saurabhjn76/sympy,asm666/sympy,debugger22/sympy,AunShiLord/sympy,Mitchkoens/sympy,bukzor/sympy,kmacinnis/sympy,AunShiLord/sympy,Gadal/sympy,saurabhjn76/sympy,jamesblunt/sympy,drufat/sympy,aktech/sympy,MridulS/sympy,farhaanbukhsh/sympy,souravsingh/sympy,shipci/sympy,maniteja123/sympy,abloomston/sympy,asm666/sympy,flacjacket/sympy,mcdaniel67/sympy,srjoglekar246/sympy,sahilshekhawat/sympy,atsao72/sympy,kaushik94/sympy,ahhda/sympy,Davidjohnwilson/sympy,dqnykamp/sympy,grevutiu-gabriel/sympy,moble/sympy,lidavidm/sympy,sunny94/temp,Shaswat27/sympy,Curious72/sympy,jerli/sympy,amitjamadagni/sympy,aktech/sympy,jamesblunt/sympy,garvitr/sympy,drufat/sympy,cccfran/sympy,pbrady/sympy,ahhda/sympy,Sumith1896/sympy,oliverlee/sympy,madan96/sympy,debugger22/sympy,kaichogami/sympy,beni55/sympy,jaimahajan1997/sympy,dqnykamp/sympy,vipulroxx/sympy,Vishluck/sympy,rahuldan/sympy,MridulS/sympy,kaushik94/sympy,ChristinaZografou/sympy,yukoba/sympy,Curious72/sympy,grevutiu-gabriel/sympy,Arafatk/sympy,Titan-C/sympy,iamutkarshtiwari/sympy,kevalds51/sympy,abhiii5459/sympy,sampadsaha5/sympy,Gadal/sympy,postvakje/sympy