OFFSET
2,1
COMMENTS
For every prime p>2, p^3 divides (p-1)^(p^2)+1 and furthermore p divides all numbers n>1 such that n^3 divides (p-1)^(n^2)+1.
a(27)>10^15. - Max Alekseyev, Nov 30 2017
Some further terms: a(28)-a(36) = {857, 3271, 7243979, 509, 263, 43019, 38921, 2683, 312055091}. a(38)-a(43) = {7499, 88588425539, 9689, 359, 1087, 383}. a(45)-a(61) = {931417, 40597, 2111, 2677, 14983, 261061, 1302937, 479, 17935703, 503, 4227137, 39398453, 2153, 1627, 1109, 28663, 1699}. a(63)-a(69) = {1229, 1867, 78877, 500861, 1987, 62683, 2777}. a(71)-a(75) = {275884327, 719, 44041, 3122698559, 15161}. a(77)-a(80) = {907927, 202471, 5788837, 16361}.
a(n) <= A177996(n).
FORMULA
a(n) = smallest prime divisor of (p-1)^(p^2)+1 other than p, where p=A000040(n).
EXAMPLE
a(2) = A127263(3)/3 = 57/3 = 19.
MATHEMATICA
a[n_] := Module[{p, k}, p = Prime[n]; k = p + 1;
While[! Divisible[(p - 1)^(k p)^2 + 1, (k p)^3], k++]; k];
Table[a[n], {n, 2, 15}] (* Robert Price, Mar 23 2020 *)
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Alexander Adamchuk, Mar 30 2007, Mar 31 2007, Apr 09 2007
EXTENSIONS
a(16)-a(26), a(39), a(74) from Max Alekseyev, May 16 2010
STATUS
approved