OFFSET
1,2
COMMENTS
Equivalently n is the number of As in a prime P of the form AAA...AA+1 where A=46. n is also equal to half the number of digits in P. The first 11 numbers of the sequence are validated by D. Alpern's java applet (see link).
Equivalently primes of the form (100^n - 1) * 46/99 + 1. - Charles R Greathouse IV, Jan 22 2015
a(12) proved prime with Primo 3.0.7. - Charles R Greathouse IV, Jan 22 2015
LINKS
Dario A. Alpern, Factorization using the Elliptic Curve Method.
EXAMPLE
47 is prime, so 1 is in the sequence.
4647 is not prime, so 2 is not in the sequence.
464647 is prime, so 3 is in the sequence.
46464647 is prime, so 4 is in the sequence.
PROG
(PARI) isok(n) = isprime(1 + 46*sum(k=1, n, 100^(k-1))); \\ Michel Marcus, Jan 22 2015
(PARI) is(n)=ispseudoprime(46*(100^n-1)/99+1) \\ Charles R Greathouse IV, Jan 22 2015
(PFGW) ABC2 46*(100^$a-1)/99+1
a: from 1 to 10000
Charles R Greathouse IV, Jan 22 2015
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Mohsen Hozan, Jan 21 2015
EXTENSIONS
a(13)-a(14) from Charles R Greathouse IV, Jan 22 2015
a(15) from Charles R Greathouse IV, Jan 23 2015
a(16)-a(17) from Charles R Greathouse IV, Jan 26 2015
STATUS
approved