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A343703
Numbers k such that k=x*y for some x and y such that x+y and the concatenation of x and y are both prime.
2
1, 4, 6, 10, 12, 18, 22, 24, 28, 30, 40, 42, 46, 48, 52, 54, 58, 60, 66, 70, 72, 76, 78, 82, 84, 88, 90, 102, 106, 112, 114, 126, 130, 132, 136, 138, 142, 148, 150, 154, 156, 162, 168, 172, 180, 184, 186, 190, 192, 196, 198, 204, 208, 210, 220, 222, 228, 232, 238, 246, 252, 258, 262, 268, 274
OFFSET
1,2
COMMENTS
All terms except 1 are even.
Includes p-1 if p is a prime such that 10*p-9 is prime.
LINKS
EXAMPLE
a(5) = 12 is a term because 12 = 4*3 where both 43 and 4+3=7 are prime.
MAPLE
filter:= proc(m) local d, e;
for d in numtheory:-divisors(m) do
e:= m/d;
if isprime(d*10^(1+ilog10(e))+e) and isprime(d+e) then return true fi
od;
false
end proc:
select(filter, [$1..1000]);
CROSSREFS
Sequence in context: A108724 A243864 A024995 * A086298 A144761 A295523
KEYWORD
nonn,base
AUTHOR
J. M. Bergot and Robert Israel, Apr 26 2021
STATUS
approved