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A339958
Composite numbers that are the sum of an even square > 0 and an odd square.
0
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
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
KEYWORD
nonn
AUTHOR
Wesley Ivan Hurt, Dec 25 2020
STATUS
approved