A269841 Integers n such that A000330(n) is the sum of 2 nonzero squares.

2, 12, 24, 25, 26, 48, 50, 60, 73, 74, 96, 97, 120, 121, 122, 145, 146, 156, 169, 194, 204, 240, 242, 289, 312, 337, 338, 348, 361, 362, 410, 432, 457, 480, 492, 529, 554, 578, 600, 624, 673, 722, 732, 768, 793, 842, 865, 866, 876, 960, 961, 985

Offset

1,1

Comments

Corresponding square pyramidal numbers are 5, 650, 4900, 5525, 6201, 38024, 42925, 73810, 132349, 137825, 299536, 308945, 583220, 597861, 612745, 1026745, ...

Links

Table of n, a(n) for n=1..52.

Example

12 is a term because A000330(12) = 1^2 + 2^2 + ... + 11^2 + 12^2 = 650 = 5^2 + 25^2.

Mathematica

Select[Range@ 1000, SquaresR[2, Binomial[# + 2, 3] + Binomial[# + 1, 3]] > 0 &] (* Michael De Vlieger, Mar 06 2016 *)

Prog

(PARI) isA000404(n) = {for( i=1, #n=factor(n)~%4, n[1, i]==3 && n[2, i]%2 && return); n && ( vecmin(n[1, ])==1 || (n[1, 1]==2 && n[2, 1]%2)); }
for(n=0, 1e3, if(isA000404(n*(n+1)*(2*n+1)/6), print1(n, ", ")));

Crossrefs

Cf. A000330, A000404.

Sequence in context: A365500 A117301 A141079 * A144551 A174457 A353011

Adjacent sequences: A269838 A269839 A269840 * A269842 A269843 A269844

Keyword

nonn

Author

Altug Alkan, Mar 06 2016

Status

approved