login
A227126
Primes p_i such that 2^(i+1) - p_i is also prime.
4
2, 3, 5, 11, 17, 167, 193, 197, 433, 4111, 9173, 42929, 95279, 98897, 139409, 142567, 228617, 329333, 344209, 791191, 829177
OFFSET
1,1
COMMENTS
The corresponding primes 2^(i + 1) - prime(i) are 2, 5, 11, 53, 239, 1099511627609, 35184372088639, ...
The prime indices i are 1, 2, 3, 5, 7, 39, 44, 45, 84, 566, 1137, ...
EXAMPLE
5 is a term because 5 is the 3rd prime, and 2^(3+1) - 5 = 16 - 5 = 11 which is a prime
11 is in the sequence because 11 = prime(5) and 2^(5 + 1) - 11 = 64 - 11 = 53 is a prime.
MATHEMATICA
p = 2; lst = {}; While[p < 850001, If[ PrimeQ[ 2^(PrimePi@ p +1) - p], AppendTo[lst, p]; Print@ p]; p = NextPrime@ p]; lst (* Robert G. Wilson v, Jul 09 2014 *)
PROG
(PARI) lista(nn) = {ip = 1; forprime(p=2, nn, if (isprime(2^(ip+1)-p), print1(p, ", ")); ip++; ); } \\ Michel Marcus, Jul 12 2014
CROSSREFS
Sequence in context: A286268 A359630 A244914 * A057652 A025067 A024371
KEYWORD
nonn,more
AUTHOR
Gerasimov Sergey, Jul 02 2013
EXTENSIONS
a(3), a(6), a(8)- a(12) from Joerg Arndt, Jul 03 2013
Corrected and extended through a(21) by Robert G. Wilson v, Jul 09 2014
Entry revised by N. J. A. Sloane, Jan 02 2019, incorporating data from a later submission from Robert G. Wilson v
STATUS
approved