A359845 Centered triangular numbers which are products of four distinct primes.

9010, 20710, 39610, 67735, 91885, 108946, 163846, 191710, 197110, 237010, 243010, 293710, 307135, 342010, 349210, 409510, 461206, 466210, 474610, 488206, 526585, 544510, 619210, 625006, 640594, 656374, 678385, 688510, 698710, 708985, 789526, 890506, 934966, 985366, 992674, 1039585

Offset: 1

Author

Massimo Kofler, Jan 15 2023

Keywords

• nonn

Comments

A squarefree subsequence of centered triangular numbers.

Examples

			9010 = 2 * 5 * 17 * 53 = (3 * 78 * (78 - 1) / 2) + 1.
20710 = 2 * 5 * 19 * 109 = (3 * 118 * (118 - 1) / 2) + 1.
39610 = 2 * 5 * 17 * 233 = (3 * 163 * (163 - 1) / 2) + 1.
		

Crossrefs

Intersection of A005448 and A046386.

Programs

Mathematica

Select[Table[3*n*(n - 1)/2 + 1, {n, 1, 1000}], FactorInteger[#][[;; , 2]] == {1, 1, 1, 1} &] (* Amiram Eldar, Jan 15 2023 *)