1,2

a(6) is unknown. a(7)-a(12) = {771936328432730777189183517369830159827426282764863750131729657829597399846468418688727, 98526125335693359373, 339448671314611904643504117119, 37589973457545958193355599, 1136272165922724266740722458520499, 480250763996501976790165756943039}.

a(6) = 11^22420 - 2 was found by Rick L. Shepherd 09/29/2007. It has 23349 decimal digits and it is too large to include. Correspondingly, the least numbers k>(2n-1) such that (2n-1)^k - 2 is prime are listed in A133856(n) = {0, 4, 14, 8, 11, 22420, 78, 17, 24, 20, 25, 24, 63, 30, 42, 69, 128, 50, 119, 204, ...}.

Henri Lifchitz & Renaud Lifchitz : PRP Records. Probable Primes Top 10000.

Cf. A084714 = smallest prime of the form (2n-1)^k - 2, or 0 if no such number exists. Cf. A014224, A109080, A090669.

Cf. A128455, A128457, A128458, A128459, A128460, A128461. Cf. A133858, A133982. Cf. A133856 = least number k>(2n-1) such that (2n-1)^k - 2 is prime, or 0 if no such number exists.

Sequence in context: A138917 A116327 A060711 this_sequence A093404 A031136 A050456

Adjacent sequences: A128469 A128470 A128471 this_sequence A128473 A128474 A128475

nonn

Alexander Adamchuk (alex(AT)kolmogorov.com), Mar 14 2007, Oct 01 2007