1,3

It appears that 1528 is the largest of 306 positive integers not in this sequence.

Table of n, a(n) for n=1..73.

Index entries for sequences related to sums of squares

Index to sequences related to pyramidal numbers

Exponents in expansion of Product_{k>=1} (1 + x^(k*(k+1)*(2*k+1)/6)).

20 is in the sequence because 20 = 1 + 5 + 14 = 1^2 + 1^2 + 2^2 + 1^2 + 2^2 + 3^2.

max = 200; f[x_] := Product[1 + x^(k (k + 1) (2 k + 1)/6), {k, 1, 10}]; Exponent[#, x] & /@ List @@ Normal[Series[f[x], {x, 0, max}]]

Cf. A000330, A003995.

Sequence in context: A314292 A294572 A084381 * A335785 A266304 A308839

Adjacent sequences: A289892 A289893 A289894 * A289896 A289897 A289898

nonn

Ilya Gutkovskiy, Jul 14 2017

approved