A357678 - OEIS

%I #13 Oct 09 2022 20:32:19

%S 8,17,107

%N Numbers k equal to the integer log of the sum of k and its digit reversal.

%C 10^n + 7 is a term if 10^n + 1 is prime, however that is conjectured to occur only for n = 0, 1 and 2.

%C No further terms < 2*10^8.

%e a(3) = 107 is a term because the integer log of (107 + 701 = 808 = 2^3*101) is 3*2 + 101 = 107.

%p rev:= proc(n) local L,i; L:= convert(n,base,10): add(L[-i]*10^(i-1),i=1..nops(L)) end proc:

%p filter:= proc(n) local s,t;

%p    s:= n + rev(n);

%p    n = add(t[1]*t[2],t=ifactors(s)[2])

%p end proc:

%p select(filter, [$1..10^6]);

%Y Cf. A001414, A004086, A056964.

%K nonn,base,bref,more

%O 1,1

%A _J. M. Bergot_ and _Robert Israel_, Oct 08 2022