■三角数,三乗数,五乗数(その2)
[1]3S(5,n)はいつもS(3,n)で割り切れる.
3S(5,n)/S(3,n)=n^2(n+1)^2(2n^2+2n−1)/4・4/n^2(n+1)^2=(2n^2+2n−1)
[2]S(3,n)はいつもS(1,n)で割り切れる.
S(3,n)/S(1,n)=n^2(n+1)^2/4・2/n(n+1)=n(n+1)/2=S(1,n)
[3]T=k(k+2)/12{6k^3+18k^2+14k+2}
=k(k+1)(k+2)(3k^2+6k+1)/6
S(1,n)=Σk=n(n+1)/2
S(2,n)=Σk^2=n(n+1)(2n+1)/6
S(3,n)=Σk^3=n^2(n+1)^2/4
S(4,n)=Σk^4=n(n+1)(2n+1)(3n^2+3n−1)/30
S(5,n)=Σk^5=n^2(n+1)^2(2n^2+2n−1)/12
S(6,n)=Σk^6=n(n+1)(2n+1)(3n^4+6n^3−3n+1)/42
S(6,n)=Σk^7=n^2(n+1)^2(3n^4+6n^3−n^2−4n+2)/24
であるが,このなかに因数(3k^2+6k+1)はみあたらない.
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