A209190 Least prime factor of reversal of digits of n.

1, 2, 3, 2, 5, 2, 7, 2, 3, 1, 11, 3, 31, 41, 3, 61, 71, 3, 7, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 13, 23, 3, 43, 53, 3, 73, 83, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 5, 3, 5, 5, 3, 5, 5, 3, 5, 5, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 7, 17, 3, 37, 47, 3, 67, 7, 3, 97, 2, 2, 2

Offset: 1

Author

N. J. A. Sloane, Mar 05 2012

Keywords

• nonn
• base
• look

Comments

This is to lpf (A020639) as A210437 is to gpf (A006530). - Jonathan Vos Post, Mar 22 2012

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..12000
• PrimeFan, Listing of Esoteric Integer Sequences
• PrimeFan, Esoteric Integer Sequences [Cached copy]

Crossrefs

Cf. A004086, A020639, A210437.

Programs

Maple

read("transforms") ;
A209190 := proc(n)
        A020639(digrev(n)) ;
end proc:
seq(A209190(n),n=1..100) ; # R. J. Mathar, Mar 22 2012

Mathematica

a[n_] := FactorInteger[IntegerReverse[n]][[1, 1]];
Array[a, 100] (* Jean-François Alcover, Jan 14 2021 *)

PARI

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

Formula

a(n) = A020639(A004086(n)) = lpf(R(n)). - Jonathan Vos Post, Mar 22 2012