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A345198
Primes p such that p-2 is the product of two emirps.
1
223, 631, 1471, 2203, 2671, 3319, 4513, 4621, 5059, 5179, 8929, 9643, 9661, 11131, 11149, 12391, 12781, 12841, 14143, 14341, 14419, 15511, 15823, 15901, 16369, 17359, 19333, 19489, 19603, 19801, 20269, 20929, 21031, 22531, 23593, 23929, 24571, 25339, 25939, 26209, 29173, 29599, 29803, 30103
OFFSET
1,1
COMMENTS
All terms == 1 (mod 6).
LINKS
EXAMPLE
a(3) = 1471 is a term because 1471-2 = 13*113, and 13 and 113 are both emirps.
MAPLE
revdigs:= proc(n) local L, i;
L:= convert(n, base, 10);
add(L[-i]*10^(i-1), i=1..nops(L))
end proc:
filter:= proc(p) local F, q, t;
if not isprime(p) then return false fi;
F:= ifactors(p-2)[2];
if add(t[2], t=F) <> 2 then return false fi;
andmap(proc(t) local s; s:= revdigs(t); s <> t and isprime(s) end proc, map(t->t[1], F))
end proc:
select(filter, [seq(i, i=1..100000, 6)]);
CROSSREFS
Cf. A006567.
Sequence in context: A142437 A142773 A096660 * A094459 A108819 A158226
KEYWORD
nonn,base
AUTHOR
J. M. Bergot and Robert Israel, Jun 10 2021
STATUS
approved