OFFSET
1,1
COMMENTS
Semiprimes with even digits are less numerous than those with odd digits, cf. A091296.
"Semiprimes with even digits are less numerous than those with odd digits" because (base 10): no integer after 10 can end in a 0 without being divisible by 2, 5 and at least one other prime; for a semiprime to end in 2, 4, 6, or 8 it must be divisible by 2 and a prime with almost as many digits as the semiprime (and primes get rarer as they get longer); no semiprime with all even digits after 22 can be a repdigit; and similar constraints. - Jonathan Vos Post, Nov 07 2005
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
MAPLE
f:= proc(n) local L, x, i;
L:= convert(n, base, 5);
x:= 2*add(L[i]*10^(i-1), i=1..nops(L));
if isprime(x/2) then x else NULL fi
end proc:
map(f, [$1..1000]); # Robert Israel, Oct 01 2024
MATHEMATICA
Select[Range[6000], Plus@@Last/@FactorInteger[ # ]==2&&Union[EvenQ/@IntegerDigits[ # ]]=={True}&]
CROSSREFS
KEYWORD
AUTHOR
Zak Seidov, Jun 14 2005
STATUS
approved