1,1

J. K. Andersen, Consecutive Congruent Primes.

a(3) = 15823 because this number is the first in a sequence of 3 consecutive primes all of the form 9n + 1.

NextPrime[ n_Integer ] := Module[ {k = n + 1}, While[ ! PrimeQ[ k ], k++ ]; Return[ k ] ]; PrevPrime[ n_Integer ] := Module[ {k = n - 1}, While[ ! PrimeQ[ k ], k-- ]; Return[ k ] ]; p = 0; Do[ a = Table[ -1, {n} ]; k = Max[ 1, p ]; While[ Union[ a ] != {1}, k = NextPrime[ k ]; a = Take[ AppendTo[ a, Mod[ k, 9 ] ], -n ] ]; p = NestList[ PrevPrime, k, n ]; Print[ p[ [ -2 ] ] ]; p = p[ [ -1 ] ], {n, 1, 7} ] a(8) > 1655036000.

Sequence in context: A159248 A158583 A009081 this_sequence A027406 A053116 A158211

Adjacent sequences: A057641 A057642 A057643 this_sequence A057645 A057646 A057647

nonn

Robert G. Wilson v (rgwv(AT)rgwv.com), Oct 11 2000

More terms from Jens Kruse Andersen (jens.k.a(AT)get2net.dk), May 31 2006