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

1,1

Comments

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

Links

Table of n, a(n) for n=1..40.

Example

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.

Mathematica

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

Crossrefs

Intersection of A007304 and A001844.

Cf. A027862, A371016, A370795.

Sequence in context: A083738 A265237 A355305 * A374269 A291602 A275881

Adjacent sequences: A380879 A380880 A380881 * A380883 A380884 A380885

Keyword

nonn,new

Author

Massimo Kofler, Feb 07 2025

Status

approved