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

Author

Clark Kimberling, Aug 02 2006

Keywords

• nonn
• easy

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

Examples

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

Links

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

Formula

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