A126950 a(1) = 1; for n>1, a(n) = the smallest number p > a(n-1) such that (a(n-1)+p)/2 is a cube.

1, 15, 39, 89, 161, 271, 415, 609, 849, 1151, 1511, 1945, 2449, 3039, 3711, 4481, 5345, 6319, 7399, 8601, 9921, 11375, 12959, 14689, 16561, 18591, 20775, 23129, 25649, 28351, 31231, 34305, 37569, 41039, 44711, 48601, 52705, 57039, 61599, 66401

Offset

1,2

Links

Table of n, a(n) for n=1..40.

Formula

a(n) = ((2*n +1)*(2*n^2 + 2*n -1)+ 5*(-1)^n)/4; a(n) = a(n-1)+2n^3; G.f. = (1 - 2*x + 14*x^2 - 2*x^3 + x^4)/((1 + x)(1 - x)^4).

Mathematica

Table[((2*n +1)*(2*n^2 + 2*n -1)+ 5*(-1)^n)/4, {n, 83}]

Crossrefs

Cf. A081352, A126938.

Sequence in context: A146696 A186295 A259429 * A091847 A062222 A369720

Adjacent sequences: A126947 A126948 A126949 * A126951 A126952 A126953

Keyword

nonn

Author

Zak Seidov, Mar 18 2007

Status

approved