login
A356095
Tetrahedral (or triangular pyramidal) numbers which are products of three distinct primes (or sphenic numbers).
0
165, 286, 455, 969, 1771, 4495, 9139, 12341, 32509, 176851, 437989, 657359, 939929, 3737581, 9290431, 21084251, 26536591, 39338069, 44101441, 61690919, 92568571, 112805879, 289442201, 381588019, 439918931, 495593039, 711215371, 815946449, 1008077071, 1103914379
OFFSET
1,1
COMMENTS
A squarefree subsequence of tetrahedral numbers a(n) = C(n+2,3) = n*(n+1)*(n+2)/6.
EXAMPLE
165 = 9*10*11/6 = 3*5*11
286 = 11*12*13/6 = 2*11*13
455 = 13*14*15/6 = 5*7*13
9139 = 37*38*39/6 = 13*19*37
MATHEMATICA
Select[Table[n*(n + 1)*(n + 2)/6, {n, 1, 2000}], FactorInteger[#][[;; , 2]] == {1, 1, 1} &] (* Amiram Eldar, Jul 26 2022 *)
CROSSREFS
Intersection of A000292 and A007304.
Subsequence of A070755.
Sequence in context: A319328 A301970 A176877 * A323379 A215967 A029563
KEYWORD
nonn
AUTHOR
Massimo Kofler, Jul 26 2022
STATUS
approved