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A089993 Penultimate prime divisor of numbers that are not powers of primes (A024619).

%I A089993 #13 Apr 14 2021 10:14:04
%S A089993 2,2,2,2,3,2,2,3,2,2,2,2,3,3,2,5,2,2,3,2,3,2,3,2,2,2,3,2,2,5,2,3,2,3,
%T A089993 2,3,5,3,2,3,5,2,2,3,2,7,3,2,2,3,5,2,3,2,3,7,2,3,2,5,2,2,3,2,3,2,5,2,
%U A089993 2,5,3,2,3,5,2,3,2,7,3,2,3,2,3,3,5,3,7,2,3,2,3,5,3,2,11,2,5,2,3,2,3,2,3,7,5
%N A089993 Penultimate prime divisor of numbers that are not powers of primes (A024619).
%H A089993 Amiram Eldar, <a href="/A089993/b089993.txt">Table of n, a(n) for n = 1..10000</a>
%F A089993 a(n) = A076820(A024619(n)). - _Amiram Eldar_, Apr 12 2021
%t A089993 Select[Table[If[Length[(f = FactorInteger[n])] > 1, f[[-2, 1]], 1], {n, 1, 150}], # > 1 &]
%o A089993 (PARI) f(n) = a=factor(n);v=a[,1];ln=length(v);if(ln>1,return(v[ln-1]));
%o A089993 g(m) = for(x=2,m,if(f(x)>0,print1(f(x)",")))
%Y A089993 Cf. A024619, A076820, A089992.
%K A089993 nonn
%O A089993 1,1
%A A089993 _Cino Hilliard_, Jan 14 2004
%E A089993 Offset corrected by _Amiram Eldar_, Apr 12 2021