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A121489
Diagonal of array A121490.
2
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
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
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Aug 02 2006
STATUS
approved