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A076886 Smallest palindrome with exactly n prime factors (counted with multiplicity).

%I A076886 #44 Oct 06 2020 14:42:10
%S A076886 1,2,4,8,88,252,2772,27872,2112,4224,8448,44544,48384,2977792,
%T A076886 27011072,405504,4091904,441606144,405909504,886898688,677707776,
%U A076886 4285005824,276486684672,21128282112,633498894336,2701312131072,6739855589376,29142024192,65892155129856
%N A076886 Smallest palindrome with exactly n prime factors (counted with multiplicity).
%C A076886 2^n <= A239697(n) <= a(n). - _Michael S. Branicky_, Oct 02 2020
%H A076886 Andrew Howroyd, <a href="/A076886/b076886.txt">Table of n, a(n) for n = 0..50</a> (terms 0..30 from Michael S. Branicky and terms 31..35 from David A. Corneth)
%H A076886 Andrew Howroyd, <a href="/A076886/a076886.txt">PARI Program</a>
%e A076886 a(4)=88 because 88 is the smallest palindromic number with 4 prime factors, 2^3*11 (counted with multiplicity).
%o A076886 (Python)
%o A076886 from sympy import factorint
%o A076886 def A076886(n):
%o A076886   d = 1
%o A076886   while True:
%o A076886     half = (d+1)//2
%o A076886     for left in range(10**(half-1), 10**half):
%o A076886       strleft = str(left)
%o A076886       if d%2 == 0:
%o A076886         m = int(strleft + strleft[::-1])
%o A076886       else:
%o A076886         m = int(strleft + (strleft[:-1])[::-1])
%o A076886         if sum(list(factorint(m).values())) == n:
%o A076886           return m
%o A076886     d += 1
%o A076886 print([A076886(n) for n in range(17)]) # _Michael S. Branicky_, Oct 02 2020
%Y A076886 Cf. A239697.
%K A076886 base,nonn
%O A076886 0,2
%A A076886 _Shyam Sunder Gupta_, Nov 25 2002
%E A076886 Edited and extended by _Robert G. Wilson v_, Dec 02 2002
%E A076886 a(26) corrected and a(27)-a(28) from _Michael S. Branicky_, Oct 02 2020