A115976 Numbers k that divide 2^(k-2) + 1.

1, 3, 49737, 717027, 9723611, 21335267, 32390921, 38999627, 43091897, 86071337, 101848553, 102361457, 228911411, 302948067, 370219467, 393664027, 455781089, 483464027, 1040406177, 1272206987, 2371678553, 2571052241, 2648052857, 3054713937, 3597613307, 3782971499, 3917903851, 4005163577, 5419912241

Offset: 1

Author

Max Alekseyev, Mar 15 2006

Keywords

• nonn

Comments

Some larger terms: 4465786944074559659, 1440261542571735083956640176981881665928575750093930787551969

Links

• Max Alekseyev, Table of n, a(n) for n = 1..708 (contains all terms below 10^15)

Crossrefs

The odd elements of A244673.

Cf. A006521, A006517, A069927, A067945, A067946, A067947, A068382, A068383, A014945, A014946, A014949, A092028.

Programs

Mathematica

lst = {}; Do[ If[ PowerMod[2, 2n - 3, 2n - 1] == 2n - 2, AppendTo[lst, 2n - 1]], {n, 10^9}]; lst (* Robert G. Wilson v, Apr 04 2006 *)

Extensions

More terms from Robert G. Wilson v, Apr 04 2006

Terms a(24) onward from Max Alekseyev, Feb 03 2015

b-file corrected and extended by Max Alekseyev, Oct 27 2018