OFFSET
1,1
COMMENTS
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.
No further terms < 2*10^8.
EXAMPLE
a(3) = 107 is a term because the integer log of (107 + 701 = 808 = 2^3*101) is 3*2 + 101 = 107.
MAPLE
rev:= proc(n) local L, i; L:= convert(n, base, 10): add(L[-i]*10^(i-1), i=1..nops(L)) end proc:
filter:= proc(n) local s, t;
s:= n + rev(n);
n = add(t[1]*t[2], t=ifactors(s)[2])
end proc:
select(filter, [$1..10^6]);
CROSSREFS
KEYWORD
nonn,base,bref,more
AUTHOR
J. M. Bergot and Robert Israel, Oct 08 2022
STATUS
approved