A121944 Composite number of the form 4n^2+1.

65, 145, 325, 485, 785, 901, 1025, 1157, 1445, 1765, 1937, 2117, 2305, 2501, 2705, 3365, 3601, 3845, 4097, 4625, 4901, 5185, 5777, 6085, 6401, 6725, 7397, 7745, 8465, 9217, 9605, 10001, 10405, 10817, 11237, 11665, 12545, 12997, 13925, 14885, 16385

Offset: 1

Author

Tanya Khovanova, Sep 03 2006

Keywords

• nonn
• easy

Crossrefs

a(n) are elements of A053755 = 4*n^2 + 1, beside 1 that are not prime, that is they do not lie in A002496 = Primes of form n^2 + 1.

Programs

Mathematica

Select[Table[4n^2 + 1, {n, 70}], ! PrimeQ[ # ] &]

Formula

a(n) ~ 4n^2 + O(n^2/log n). - Charles R Greathouse IV, Oct 24 2022