OFFSET
1,1
COMMENTS
All terms == 1 (mod 6).
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
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
KEYWORD
nonn,base
AUTHOR
J. M. Bergot and Robert Israel, Jun 10 2021
STATUS
approved