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A108636
Semiprimes with even digits.
2
4, 6, 22, 26, 46, 62, 82, 86, 202, 206, 226, 262, 422, 446, 466, 482, 622, 626, 662, 802, 842, 862, 866, 886, 2026, 2042, 2062, 2066, 2206, 2246, 2402, 2426, 2446, 2462, 2602, 2606, 2642, 2846, 2866, 4006, 4022, 4222, 4226, 4262, 4282, 4286, 4406, 4426, 4442
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
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
Intersection of A001358 and A014263.
Cf. A091296.
Sequence in context: A286358 A088228 A272309 * A101143 A083157 A192154
KEYWORD
nonn,base,look
AUTHOR
Zak Seidov, Jun 14 2005
STATUS
approved