A209190 - OEIS

%I #40 Jan 14 2021 04:52:37

%S 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,

%T 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,

%U 2,2,2,2,2,2,7,17,3,37,47,3,67,7,3,97,2,2,2

%N Least prime factor of reversal of digits of n.

%C This is to lpf (A020639) as A210437 is to gpf (A006530). - _Jonathan Vos Post_, Mar 22 2012

%H Alois P. Heinz, <a href="/A209190/b209190.txt">Table of n, a(n) for n = 1..12000</a>

%H PrimeFan, <a href="http://primefan.tripod.com/EsotericIntegerSequences.html">Listing of Esoteric Integer Sequences</a>

%F a(n) = A020639(A004086(n)) = lpf(R(n)). - _Jonathan Vos Post_, Mar 22 2012

%p read("transforms") ;

%p A209190 := proc(n)

%p         A020639(digrev(n)) ;

%p end proc:

%p seq(A209190(n),n=1..100) ; # _R. J. Mathar_, Mar 22 2012

%t a[n_] := FactorInteger[IntegerReverse[n]][[1, 1]];

%t Array[a, 100] (* _Jean-François Alcover_, Jan 14 2021 *)

%o (PARI) lpf(n) = if (n==1, 1, vecmin(factor(n)[,1]));

%o a(n) = lpf(fromdigits(Vecrev(digits(n)))); \\ _Michel Marcus_, Feb 11 2020

%Y Cf. A004086, A020639, A210437.

%K nonn,base,look

%O 1,2

%A _N. J. A. Sloane_, Mar 05 2012