A256587 Number of ways to write n = r + s + t, where r,s,t are elements of the set {floor(k*(k+1)/4): k = 1,2,3,...} with s odd and r <= s <= t.
0, 1, 1, 1, 1, 2, 2, 2, 3, 2, 4, 2, 4, 2, 5, 3, 4, 3, 3, 5, 3, 4, 2, 6, 2, 4, 1, 6, 2, 4, 1, 4, 2, 3, 3, 2, 3, 1, 3, 2, 4, 1, 3, 1, 3, 2, 4, 1, 3, 1, 3, 1, 4, 2, 4, 1, 3, 2, 3, 3, 3, 3, 2, 3, 2, 5, 4, 3, 3, 4, 3, 5, 5, 4, 3, 5, 3, 6, 6, 5, 4, 7, 3, 6, 4, 7, 4, 8, 3, 7, 5, 6, 7, 6, 5, 6, 6, 6, 7, 8
Offset: 1
Keywords
Examples
a(27) = 1 since 27 = 0 + 5 + 22 = floor(1*2/4) + floor(4*5/4) + floor(9*10/4). a(56) = 1 since 56 = 1 + 3 + 52 = floor(2*3/4) + floor(3*4/4) + floor(14*15/4).
Links
- Zhi-Wei Sun, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
S[n_]:=Union[Table[Floor[k*(k+1)/4],{k,1,(Sqrt[16n+13]-1)/2}]] L[n_]:=Length[S[n]] Do[r=0;Do[If[Part[S[n],x]>n/3,Goto[cc]];Do[If[Part[S[n],x]+2*Part[S[n],y]>n,Goto[bb]]; If[Mod[Part[S[n],y],2]==1&&MemberQ[S[n], n-Part[S[n],x]-Part[S[n],y]]==True,r=r+1]; Continue,{y,x,L[n]}];Label[bb];Continue,{x,1,L[n]}];Label[cc];Print[n," ",r];Continue, {n,1,100}]
Comments