A359624 Centered triangular numbers which are products of three distinct primes.

1054, 1786, 2110, 2710, 4294, 5134, 6634, 7885, 8326, 10210, 12835, 13114, 14554, 17014, 22510, 24769, 25546, 26335, 30889, 32635, 36271, 42085, 44635, 45154, 47794, 49414, 52174, 52735, 53866, 56746, 58510, 61510, 63346, 66466, 68374, 71614, 73594, 75601, 76954, 84610, 88210

Offset

1,1

Comments

A squarefree subsequence of centered triangular numbers.

Links

Table of n, a(n) for n=1..41.

Example

1054 = 2 * 17 * 31 = (3 * 27 * (27 - 1) / 2) + 1.
1786 = 2 * 19 * 47 = (3 * 35 * (35 - 1) / 2) + 1.
7885 = 5 * 19 * 83 = (3 * 73 * (73 - 1) / 2) + 1.

Mathematica

Select[Table[3*n*(n - 1)/2 + 1, {n, 1, 250}], FactorInteger[#][[;; , 2]] == {1, 1, 1} &] (* Amiram Eldar, Jan 08 2023 *)

Crossrefs

Intersection of A005448 and A007304.

Sequence in context: A353054 A090005 A339249 * A225714 A158692 A236905

Adjacent sequences: A359621 A359622 A359623 * A359625 A359626 A359627

Keyword

nonn

Author

Massimo Kofler, Jan 08 2023

Status

approved