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A263998 Number of ordered ways to write n as x^2 + 2*y^2 + p*(p+d)/2, where x and y are nonnegative integers, d is 1 or -1, and p is prime. 4
1, 1, 3, 3, 3, 3, 4, 1, 4, 4, 3, 7, 2, 4, 5, 2, 3, 4, 7, 3, 7, 5, 4, 5, 5, 3, 5, 8, 3, 8, 3, 4, 6, 5, 4, 5, 10, 2, 11, 4, 2, 6, 3, 6, 3, 7, 5, 5, 3, 3, 6, 5, 6, 8, 7, 3, 9, 5, 4, 9, 5, 4, 4, 8, 4, 5, 8, 2, 11, 5, 5, 9, 5, 6, 8, 6, 5, 10, 8, 3, 4, 13, 4, 10, 7, 4, 12, 6, 7, 4, 10, 6, 7, 6, 4, 9, 5, 5, 8, 11 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
Conjecture: a(n) > 0 for all n > 0, and a(n) = 1 only for n = 1, 2, 8.
This is similar to the conjecture in A262785.
LINKS
Zhi-Wei Sun, Some mysterious representations of integers, a message to Number Theory Mailing List, Oct. 25, 2015.
EXAMPLE
a(1) = 1 since 1 = 0^2 + 2*0^2 + 2*(2-1)/2 with 2 prime.
a(2) = 1 since 2 = 1^2 + 2*0^2 + 2*(2-1)/2 with 2 prime.
a(8) = 1 since 8 = 0^2 + 2*1^2 + 3*(3+1)/2 with 3 prime.
MATHEMATICA
SQ[n_]:=SQ[n]=IntegerQ[Sqrt[n]]
f[d_, n_]:=f[d, n]=Prime[n](Prime[n]+(-1)^d)/2
Do[r=0; Do[If[SQ[n-f[d, k]-2x^2], r=r+1], {d, 0, 1}, {k, 1, PrimePi[(Sqrt[8n+1]-(-1)^d)/2]}, {x, 0, Sqrt[(n-f[d, k])/2]}]; Print[n, " ", r]; Continue, {n, 1, 100}]
CROSSREFS
Sequence in context: A264097 A177013 A092282 * A048181 A091799 A276863
KEYWORD
nonn
AUTHOR
Zhi-Wei Sun, Oct 31 2015
STATUS
approved

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Last modified June 14 02:53 EDT 2024. Contains 373392 sequences. (Running on oeis4.)