This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A358927 #7 Feb 16 2025 08:34:04
%S A358927 1,-1,4,20,56,120,560,4960,19600,41664,341376,695520,7207200,22238720,
%T A358927 178433024,1429559296,179481600,11453245440,11444858880,393079864320,
%U A358927 3928874471424,5864598896640,46910348656640,975649558118400,3002365391929344,7805131503206400
%N A358927 a(n) is the smallest tetrahedral number with exactly n prime factors (counted with multiplicity), or -1 if no such number exists.
%H A358927 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PrimeFactor.html">Prime Factor</a>
%H A358927 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TetrahedralNumber.html">Tetrahedral Number</a>
%e A358927 a(4) = 56, because 56 is a tetrahedral number with 4 prime factors (counted with multiplicity) {2, 2, 2, 7} and this is the smallest such number.
%t A358927 t[k_] := k*(k + 1)*(k + 2)/6; a[n_] := Module[{k = 1, tk}, While[PrimeOmega[tk = t[k]] != n, k++]; tk]; a[1] = -1; Array[a, 26, 0] (* _Amiram Eldar_, Dec 09 2022 *)
%Y A358927 Cf. A000292, A001222, A075088, A156329, A279082, A358865.
%K A358927 sign
%O A358927 0,3
%A A358927 _Ilya Gutkovskiy_, Dec 06 2022