Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #5 Apr 02 2017 10:03:10
%S 1,2,3,2,5,2,7,2,2,2,11,2,13,2,3,2,17,2,19,2,3,2,23,2,2,2,3,2,29,2,31,
%T 2,3,2,5,2,37,2,3,2,41,2,43,2,2,2,47,2,2,2,3,2,53,2,5,2,3,2,59,2,61,2,
%U 2,2,5,2,67,2,3,2,71,2,73,2,2,2,7,2,79,2,2
%N Least prime number appearing in the prime tower factorization of n (when n > 1); a(1) = 1.
%C See A182318 for the definition of the prime tower factorization of a number.
%C a(n) <= A020639(n) for any n>0.
%H Rémy Sigrist, <a href="/A284694/b284694.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = A020639(A279513(n)) for any n>0.
%e 9 = 3^2, hence a(9) = min(3, 2) = 2.
%Y Cf. A020639, A182318, A279513, A284695.
%K nonn
%O 1,2
%A _Rémy Sigrist_, Apr 01 2017