OFFSET
1,1
COMMENTS
Terms > 11 with an even number of digits have an even first digit.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(6) = 23 is a term because 23 is a prime and 23 + 32 = 55 = 5 * 11 is a semiprime.
MAPLE
digrev:= proc(n) local L, i;
L:= convert(n, base, 10);
add(L[-i]*10^(i-1), i=1..nops(L))
end proc:
select(p -> isprime(p) and numtheory:-bigomega(p+digrev(p))=2, [2, seq(i, i=3..10000, 2)]);
MATHEMATICA
Select[Prime[Range[10^4]], 2 == PrimeOmega[# + FromDigits[Reverse[IntegerDigits[#]]]] &]]
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Zak Seidov and Robert Israel, Nov 30 2023
STATUS
approved