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A248334
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The subsequence of A246885 having even values.
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1
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0, 2, 4, 6, 16, 20, 32, 34, 48, 54, 58, 86, 108, 110, 124, 128, 132, 160, 162, 236, 250, 254, 256, 258, 272, 282, 310, 358, 384, 432, 436, 464, 500, 502, 506, 516, 540, 554, 628, 686, 688, 690, 718, 750, 794, 864, 866, 880, 918, 932, 942, 992, 1024, 1028, 1056
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OFFSET
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1,2
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COMMENTS
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Let f(x)=Sum(x^i^3), then 1/f(x) has coefficients given in A246885. The subsequence of A246885 having even values is A248334. This is the same as the numbers that can be written in an odd number of ways as a sum 2r^3 + 4s^3, where r and s are nonnegative integers.
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LINKS
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MAPLE
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b:= proc(n) option remember; irem(`if`(n=0, 1,
`if`(n<0, 0, add(b(n-i^3), i=1..iroot(n, 3)))), 2)
end:
a:= proc(n) option remember; local k; for k from 2+
`if`(n=1, -2, a(n-1)) by 2 while b(k)=0 do od; k
end:
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MATHEMATICA
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InverseOfCubes[m_]:=Module[{V}, V[0]=1; Do[V[i]=0, {i, 1, m}];
Reap[Sow[0];
Do[If[OddQ[Sum[V[counter-i^3], {i, 1, counter^(1/3)}]], V[counter]=1;
Sow[counter]], {counter, 1, m}]][[2, 1]]]
inv=InverseOfCubes[400];
Select[inv, EvenQ]
(* This program adapted from code written by Kevin O'Bryant *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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