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 A087173 #18 Feb 16 2025 08:32:51 %S A087173 1,2,3,5,7,11,3,2,2,2,2,7,101,3,2,3,3,5,2,3,2,2,5,3,2,2,2,2,5,2,2,3,3, %T A087173 2,3,17977,7,5,3,2,3,2,3,5,2,2,2,3,5,2,3,3,3,5,2,11,2,2,2,17,3,2,3,2, %U A087173 2,2,1181,3,5,2,3,11,23,2,2,7,10619863,2,2,2,11,5,7,2,11,2,11,3,5,2473 %N A087173 Smallest prime factor of n-th partition number. %H A087173 Giovanni Resta, <a href="/A087173/b087173.txt">Table of n, a(n) for n = 1..10000</a> %H A087173 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/LeastPrimeFactor.html">Least Prime Factor</a> %H A087173 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PartitionFunction.html">Partition Function</a> %H A087173 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PartitionFunctionPCongruences.html">Partition Function P Congruences</a> %F A087173 a(n) = A020639(A000041(n)). %e A087173 A000041(100) = 190569292 = 2*2*43*59*89*211, therefore a(100)=2. %t A087173 FactorInteger[#][[1,1]]&/@PartitionsP[Range[90]] (* _Harvey P. Dale_, May 20 2023 *) %o A087173 (PARI) spf(n) = if (n==1, 1, vecmin(factor(n)[,1])); %o A087173 a(n) = spf(numbpart(n)); \\ _Michel Marcus_, Feb 24 2023 %Y A087173 Cf. A071963. %K A087173 nonn %O A087173 1,2 %A A087173 _Reinhard Zumkeller_, Aug 23 2003