A121489 Diagonal of array A121490.

3, 1, 9, 17, 19, 9, 18, 17, 55, 24, 38, 36, 12, 65, 106, 129, 128, 97, 30, 100, 148, 168, 154, 100, 251, 113, 198, 249, 260, 225, 138, 356, 163, 297, 389, 433, 423, 353, 217, 9, 248, 441, 17, 80, 79, 8, 506, 297, 687, 316, 574, 17, 119, 145, 89, 784, 568, 252, 737

Offset

1,1

Comments

Also, a(n) is the smallest positive integer such that n^3 + a(n) is a square. [Bruno Berselli, Jan 29 2013]

For n = m^2, a(n) = 2*m^3 + 1; e.g., a(1) = 2*1^3 + 1 = 3, a(4) = 2*2^3 + 1 = 17, a(9) = 2*3^3 + 1 = 55; otherwise a(n) < 2*(n^(3/2) + 1. - Zak Seidov, Mar 24 2013

Links

Zak Seidov, Table of n, a(n) for n = 1..10000

Formula

a(n) = floor(n^(3/2) + 1)^2 - n^3.

Example

a(2) = floor(2^(3/2) + 1)^2 - 2^3 = 9 - 8 = 1.

Crossrefs

Sequence in context: A076806 A111568 A209324 * A118793 A247231 A160568

Adjacent sequences: A121486 A121487 A121488 * A121490 A121491 A121492

Keyword

nonn

Author

Clark Kimberling, Aug 02 2006

Status

approved