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A254002
Numbers n such that 1 + 46* Sum_{k=1..n} 100^(k-1) is prime.
1
1, 3, 4, 6, 9, 45, 57, 130, 142, 198, 273, 331, 2494, 8437, 10210, 17377, 19972
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
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
CROSSREFS
Cf. A110705.
Sequence in context: A293272 A192286 A242028 * A095729 A185739 A050087
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