A194639 Indices of records in A194591 when it is restricted to odd indices.

1, 5, 13, 47, 59, 109, 241, 335, 1109, 1373, 1447, 14893, 52267, 56543, 649603, 838441, 8840101, 16935761, 100604513, 118373279, 270704167, 1355477231

Offset: 1

Author

Arkadiusz Wesolowski, Aug 31 2011

Keywords

• more
• nonn

Comments

Integers for which the smallest k in A194591 such that (2*n-1)*2^k - 1 or (2*n-1)*2^k + 1 is prime (A194638) increases.

A194637 gives the record values of A194636.

References

• Wilfrid Keller, personal communication, 2010.

Links

• Chris K. Caldwell, The List of Largest Known Primes, 1355477231 * 2^356981 + 1
• Carlos Rivera, Problem 30

Crossrefs

Cf. A194591, A194600, A194603, A194606, A194607, A194608, A194635, A194636, A194637, A194638.

Cf. A064699, A076335, A180247, A217892.

Cf. A217892 (indices of records of unrestricted A194591)

Programs

Mathematica

l = -1; Flatten[Table[n = 2*n - 1; k = 0; While[! PrimeQ[n*2^k - 1] && ! PrimeQ[n*2^k + 1], k++]; If[k > l, l = k; n, {}], {n, 10^5}]] (* Arkadiusz Wesolowski, Sep 04 2011 *)

Extensions

a(22) was found in 2002 by Wilfrid Keller.

Definition corrected by Max Alekseyev and Farideh Firoozbakht, Oct 16 2014