The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A353027 Tetrahedral (or triangular pyramidal) numbers which are products of four distinct primes. 2
 1330, 6545, 16215, 23426, 35990, 39711, 47905, 52394, 57155, 79079, 105995, 138415, 198485, 221815, 246905, 366145, 477191, 762355, 1004731, 1216865, 1293699, 1373701, 1587986, 1633355, 1726669, 1823471, 1975354, 2246839, 2862209, 2997411, 3208094, 3580779, 4149466, 4590551 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A squarefree subsequence of tetrahedral numbers. LINKS Robert Israel, Table of n, a(n) for n = 1..10000 EXAMPLE 1330 = 19*20*21/6 = 2 * 5 * 7 * 19; 6545 = 33*34*35/6 = 5 * 7 * 11 * 17; 16215 = 45*46*47/6 = 3 * 5 * 23 * 47; 23426 = 51*52*53/6 = 2 * 13 * 17 * 53. MAPLE filter:= proc(n) local F; F:= ifactors(n, easy)[2]; F[.., 2] = [1, 1, 1, 1] end proc: select(filter, [seq(n*(n+1)*(n+2)/6, n=1..1000)]); # Robert Israel, Apr 18 2023 MATHEMATICA Select[Table[n*(n + 1)*(n + 2)/6, {n, 1, 300}], FactorInteger[#][[;; , 2]] == {1, 1, 1, 1} &] (* Amiram Eldar, Apr 18 2022 *) PROG (Python) from sympy import factorint from itertools import count, islice def agen(): for t in (n*(n+1)*(n+2)//6 for n in count(1)): f = factorint(t, multiple=True) if len(f) == len(set(f)) == 4: yield t print(list(islice(agen(), 34))) # Michael S. Branicky, May 28 2022 CROSSREFS Intersection of A000292 and A046386. Subsequence of A070755. Sequence in context: A205091 A038854 A323329 * A182371 A252258 A038677 Adjacent sequences: A353024 A353025 A353026 * A353028 A353029 A353030 KEYWORD nonn AUTHOR Massimo Kofler, Apr 18 2022 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 22 11:59 EDT 2023. Contains 365531 sequences. (Running on oeis4.)