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 A237912 Smallest number m (not ending in a 0) such that m and the digit reversal of m have n prime factors (counted with multiplicity). 2
 13, 15, 117, 126, 1386, 2576, 21708, 25515, 21168, 46848, 295245, 2937856, 6351048, 21989376, 217340928, 2154281472, 2196652032, 21120051456, 21122906112, 40915058688, 274148425728 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Palindromes are not included in this sequence since the reverse of a palindrome is the same number. See A076886 and A237913. a(22) > 10^12. - Giovanni Resta, Feb 23 2014 a(22) <= 21793707589632. - Chai Wah Wu, Dec 05 2014 LINKS EXAMPLE 13 and 31 are both prime so a(1) = 13. 15 and 51 have two prime factors (3*5 and 3*17 respectively), so a(2) = 15. 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 = 1 ..while n < 10**8: ....if rev(n) != n: ......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 ....else: ......n += 1 x = 1 while x < 100: ..print(RevFact(x)) ..x += 1 CROSSREFS Cf. A004086. Sequence in context: A318543 A302001 A109018 * A268664 A158697 A295151 Adjacent sequences:  A237909 A237910 A237911 * A237913 A237914 A237915 KEYWORD nonn,base,more AUTHOR Derek Orr, Feb 15 2014 EXTENSIONS a(15)-a(21) from Giovanni Resta, Feb 23 2014 STATUS approved

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Last modified June 24 20:32 EDT 2022. Contains 354830 sequences. (Running on oeis4.)