A210437 Greatest prime factor of reversal of digits of n.

1, 2, 3, 2, 5, 3, 7, 2, 3, 1, 11, 7, 31, 41, 17, 61, 71, 3, 13, 2, 3, 11, 2, 7, 13, 31, 3, 41, 23, 3, 13, 23, 11, 43, 53, 7, 73, 83, 31, 2, 7, 3, 17, 11, 3, 2, 37, 7, 47, 5, 5, 5, 7, 5, 11, 13, 5, 17, 19, 3, 2, 13, 3, 23, 7, 11, 19, 43, 3, 7, 17, 3, 37, 47, 19

Offset: 1

Author

Alois P. Heinz, Mar 21 2012

Keywords

• nonn
• look
• base

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..12000

Crossrefs

Cf. A004086, A006530, A209190.

Programs

Maple

with(numtheory):
r:= proc(n) option remember; local q;
      `if`(n<10, n, irem(n, 10, 'q')*10^(length(n)-1) +r(q))
    end:
a:= n-> `if`(r(n)=1, 1, max(factorset(r(n))[])):
seq(a(n), n=1..100);

Mathematica

FactorInteger[FromDigits[Reverse[IntegerDigits[#]]]][[-1,1]]&/@Range[80] (* Harvey P. Dale, Sep 14 2014 *)

PARI

gpf(n) = if (n==1, 1, vecmax(factor(n)[,1]));
a(n) = gpf(fromdigits(Vecrev(digits(n)))); \\ Michel Marcus, Feb 11 2020

Formula

a(n) = A006530(A004086(n)) = gpf(R(n)). - Jonathan Vos Post, Mar 22 2012