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 A359090 #18 Feb 16 2025 08:34:04 %S A359090 1,-1,2,4,6,8,14,30,48,62,126,160,350,510,1022,2046,1024,4095,4094, %T A359090 13310,28672,32768,65534,180224,262142,360448,262143,2097151,3276800, %U A359090 4194302,2097150,33554432,16777214,66715648,33554430,184549374,134217728,536870910,1073741824 %N A359090 a(n) is the index of the smallest tetrahedral number with exactly n prime factors (counted with multiplicity), or -1 if no such number exists. %H A359090 Daniel Suteu, <a href="/A359090/b359090.txt">Table of n, a(n) for n = 0..41</a> %H A359090 Lucas A. Brown, <a href="https://github.com/lucasaugustus/oeis/blob/main/A359090.py">Python program</a>. %H A359090 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PrimeFactor.html">Prime Factor</a> %H A359090 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TetrahedralNumber.html">Tetrahedral Number</a> %o A359090 (PARI) a(n) = if(n==1, return(-1)); for(k=1, oo, my(t=(k*(k+1)*(k+2))\6); if(bigomega(t) == n, return(k))); \\ _Daniel Suteu_, Dec 30 2022 %Y A359090 Cf. A000292, A001222, A076550, A358927, A359089. %K A359090 sign %O A359090 0,3 %A A359090 _Ilya Gutkovskiy_, Dec 16 2022 %E A359090 a(27)-a(34) from _Daniel Suteu_, Dec 30 2022 %E A359090 a(35)-a(38) from _Lucas A. Brown_, Sep 11 2024