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 A237913 Smallest number m > 1 (not ending in a 0) such that m and the digit reversal of m have n prime factors (counted with multiplicity). Palindromes are included. 2
 2, 4, 8, 88, 252, 2576, 21708, 2112, 4224, 8448, 44544, 48384, 2977792, 21989376, 405504, 4091904, 441606144, 405909504, 886898688, 677707776, 4285005824 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS FORMULA a(n) = min{A076886(n+1), A237912(n)} EXAMPLE 252 is the smallest number such that 252 and its reverse (also 252) have 5 prime factors (2*2*3*3*7). So, a(5) = 252. 2576 is the smallest number such that 2576 and its reverse (6752) have 6 prime factors (2*2*2*2*7*23 and 2*2*2*2*2*211, respectively). So a(6) = 2576. PROG (Python) import sympy from sympy import factorint def rev(x): ..rev = '' ..for i in str(x): ....rev = i + rev ..return int(rev) def RevFact(x): ..n = 2 ..while n < 10**8: ....if n % 10 != 0: ......if sum(list(factorint(n).values())) == x: ........if sum(list(factorint(rev(n)).values())) == x: ..........return n ........else: ..........n += 1 ......else: ........n += 1 ....else: ......n += 1 x = 1 while x < 100: ..print(RevFact(x)) ..x += 1 CROSSREFS Cf. A004086, A076886, A237912. Sequence in context: A088114 A348050 A239697 * A076886 A309565 A046385 Adjacent sequences:  A237910 A237911 A237912 * A237914 A237915 A237916 KEYWORD nonn,base,more AUTHOR Derek Orr, Feb 15 2014 EXTENSIONS a(17)-a(21) from Giovanni Resta, Feb 23 2014 STATUS approved

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Last modified August 8 14:39 EDT 2022. Contains 356009 sequences. (Running on oeis4.)