OFFSET
1,1
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(4) = 74 because A115670(4) = 47 is the 4th prime whose reversal is a semiprime, and 74 is that reversal.
MAPLE
rev:= proc(n) local L, i;
L:= convert(n, base, 10);
add(L[-i]*10^(i-1), i=1..nops(L))
end proc:
map(rev, select(p -> isprime(p) and numtheory:-bigomega(rev(p)) = 2, [seq(i, i=3..1000, 2)]);
MATHEMATICA
s = {}; Do[If[2 == PrimeOmega[sm = FromDigits[Reverse[IntegerDigits[Prime[k]]]]], AppendTo[s, sm]], {k, 200}]; s
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Zak Seidov and Robert Israel, Dec 18 2023
STATUS
approved