2,1

a(11)-a(14) = {8153, 20395, 5805311, 93929}. a(18)-a(19) = {319, 559}. a(21)-a(22) = {5053, 1535}. a(25) = 869.

a(27)-a(29) = {17473, 803, 39259}. a(32) = 95. - Alexander Adamchuk (alex(AT)kolmogorov.com), Feb 17 2007

a(15) = A128155(16) = 3736136819 and a(16) = A128156(17) = 1343851 found by Ryan Propper Feb 27-28 2007.

First term currently unknown is a(36) >= 41*10^10. [From Tyler Cadigan (tylercadigan(AT)gmail.com), Feb 21 2009]

a(n)=k must be odd since n and a(n) are of opposite parity. The only way this can occur is if k is odd. [From Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 12 2009]

Hagen von Eitzen, Table of n, a(n) for n=2..35.

Robert G. Wilson v, Table of n, a(n) for n = 2..10000 with -1 for large entries where a(n) has not yet been found [From Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 12 2009]

a(2) = A036236(3) = 4700063497.

t = Table[0, {10000}]; f[n_] := Block[{k = 1}, While[k < 2097153 && PowerMod[n, k, k] != n + 1, If[ Mod[k, 6] == 1, k += 4, k += 2]]; k]; Do[ If[ t[[n]] == 0, a = f@n; If[a < 2097153, t[[n]] = a; Print[{n, a}]]], {n, 10000}]; t [From Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 12 2009]

Cf. A036236, A078457, A119678, A119679, A127816, A119715, A119714, A127817, A127818, A127819, A127820, A127821, A128154, A128155, A128156, A128157, A128158, A128159, A128160. Cf. A128149 = Least k such that n^k (mod k) = n-1.

Sequence in context: A092776 A034916 A124977 this_sequence A050259 A015384 A072018

Adjacent sequences: A128169 A128170 A128171 this_sequence A128173 A128174 A128175

nonn

Alexander Adamchuk (alex(AT)kolmogorov.com), Feb 17 2007

a(10),a(17),a(20),a(23)-a(24),a(26),a(30)-a(31),a(33)-a(35) determined. Tyler Cadigan (tylercadigan(AT)gmail.com), Feb 21 2009

Terms corrected by Hagen von Eitzen (math(AT)von-eitzen.de) and R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 05 2009

Removed obsolete link to a-file duplicate - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 24 2009