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%I #12 Feb 26 2023 03:38:34
%S 1,2,3,11,20,84,455,1364,10659,58695,254540,728364,13516580,133595384,
%T 812646120,5327923964,68971338435,838101203939,7588384207404,
%U 69322940121435,490005293940084
%N a(n) is the index of the smallest triangular number with exactly n distinct prime factors.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/DistinctPrimeFactors.html">Distinct Prime Factors</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/TriangularNumber.html">Triangular Number</a>
%o (PARI) a(n) = my(k=1); while(omega(k*(k+1)/2) != n, k++); k; \\ _Michel Marcus_, Feb 26 2023
%Y Cf. A000217, A001221, A076550, A076551.
%K nonn,more
%O 0,2
%A _Ilya Gutkovskiy_, Dec 12 2022
%E a(19)-a(20) from _Michael S. Branicky_, Feb 25 2023
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