A380882 Centered square numbers which are sphenic numbers.

1105, 2665, 3445, 7565, 8845, 14965, 15665, 16745, 17485, 18241, 20605, 22685, 23545, 27145, 28085, 32005, 32513, 35113, 37265, 48985, 50245, 50881, 55445, 56785, 62305, 71065, 74885, 78013, 80401, 81205, 84461, 85285, 88621, 89465, 109045, 111865, 113765, 116645, 118585, 119561

Offset: 1

Author

Massimo Kofler, Feb 07 2025

Keywords

• nonn

Comments

a(n) == 1 (mod 4).

Examples

			1105 = 5 * 13* 17 which is the 24-th centered square number.
18241 = 17 * 29 * 37 which is the 96-th centered square number.
32513 = 13 * 41 * 61 which is 128-th centered square number.
		

Crossrefs

Intersection of A007304 and A001844.

Cf. A027862, A371016, A370795.

Programs

Mathematica

Select[Table[2*n*(n+1) + 1, {n, 0, 250}], FactorInteger[#][[;; , 2]] == {1, 1, 1} &] (* Amiram Eldar, Feb 07 2025 *)