A339958 Composite numbers that are the sum of an even square > 0 and an odd square.

25, 45, 65, 85, 117, 125, 145, 153, 169, 185, 205, 221, 225, 245, 261, 265, 289, 305, 325, 333, 365, 369, 377, 405, 425, 445, 477, 481, 485, 493, 505, 533, 545, 549, 565, 585, 605, 625, 629, 637, 657, 685, 689, 697, 725, 745, 765, 785, 793, 801, 833, 841, 845, 865, 873

Offset

1,1

Links

Table of n, a(n) for n=1..55.

Example

45 is in the sequence since it is composite with 3^2 + 6^2 = 9 + 36 = 45, 9 is odd and 36 is even > 0.

Mathematica

Table[If[(1 - PrimePi[n] + PrimePi[n - 1]) Sum[Sign[(Mod[i, 2] Mod[n - i + 1, 2] + Mod[i + 1, 2] Mod[n - i, 2])] (Floor[Sqrt[i]] - Floor[Sqrt[i - 1]]) (Floor[Sqrt[n - i]] - Floor[Sqrt[n - i - 1]]), {i, Floor[n/2]}] > 0, n, {}], {n, 1000}] // Flatten

Crossrefs

Cf. A002144 (Pythagorean primes), A005171.

Sequence in context: A188005 A054520 A343826 * A192261 A038811 A028505

Adjacent sequences: A339955 A339956 A339957 * A339959 A339960 A339961

Keyword

nonn

Author

Wesley Ivan Hurt, Dec 25 2020

Status

approved