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 A320445 Primes p such that 2*p-1 and the concatenation of p and 2*p-1 are primes. 1
 2, 367, 661, 691, 997, 1459, 2011, 2557, 2707, 3061, 3967, 4027, 4177, 4357, 4639, 5749, 6211, 6229, 6961, 7537, 7561, 7951, 8191, 8629, 8689, 9619, 10789, 10837, 11311, 12619, 13009, 13249, 13417, 13681, 14419, 14461, 14821, 15121, 15277, 15427, 15541, 15667, 15739, 15991, 16519, 17137, 17257 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Primes p arising in A320442. All terms but the first == 1 (mod 6). LINKS Robert Israel, Table of n, a(n) for n = 1..10000 EXAMPLE 367 is in the sequence because 367, 2*367-1=733, and 367733 are all primes. MAPLE filter:= proc(p) local q, r;    if not isprime(p) then return false fi;    q:= 2*p-1;    r:= p*10^(1+ilog10(q))+q;    isprime(r) and isprime(q); end proc: select(filter, [2, seq(i, i=7..200000, 6)]); PROG (PARI) isok(p) = isprime(p) && isprime(2*p-1) && isprime(eval(concat(Str(p), Str(2*p-1)))); \\ Michel Marcus, Jan 10 2019 CROSSREFS Cf. A320442. Sequence in context: A013506 A013512 A295174 * A142532 A329555 A171431 Adjacent sequences:  A320442 A320443 A320444 * A320446 A320447 A320448 KEYWORD nonn,base AUTHOR J. M. Bergot and Robert Israel, Jan 09 2019 STATUS approved

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Last modified November 27 16:34 EST 2021. Contains 349394 sequences. (Running on oeis4.)