A073805 - OEIS

%I #15 Jul 04 2024 02:39:13

%S 1,2,4,6,10,16,18,20,24,25,26,28,36,42,50,52,58,61,62,63,66,68,70,80,

%T 81,82,85,86,90,100,108,112,116,120,132,136,138,140,152,162,170,190,

%U 198,200,204,205,209,210,211,213,214,219,223,224,228,231,234,236,238

%N Numbers k such that 1 + k*R(k) is prime, where R(k) is the reverse of k.

%H Robert Israel, <a href="/A073805/b073805.txt">Table of n, a(n) for n = 1..10000</a>

%e 16 is a term because 16*61 + 1 = 977 is prime.

%p rev:= proc(n) local L,i;

%p   L:= convert(n,base,10);

%p   add(L[-i]*10^(i-1),i=1..nops(L))

%p end proc:

%p filter:= t -> isprime(t*rev(t)+1):

%p select(filter, [$1..1000]); # _Robert Israel_, Jul 03 2024

%t Select[Range[250],PrimeQ[# IntegerReverse[#]+1]&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Oct 05 2017 *)

%Y Cf. A004086, A061205.

%K nonn,easy,base,look

%O 1,2

%A _Shyam Sunder Gupta_, Aug 23 2002