OFFSET
1,1
COMMENTS
All prime divisors of (R^5 - 1)/(R - 1) different from 5 are congruent to 1 modulo 10.
REFERENCES
M. Ram Murty, Problems in Analytic Number Theory, Springer-Verlag, NY, (2001), pp. 208-209.
LINKS
Max Alekseyev, Table of n, a(n) for n=1..34
EXAMPLE
a(3) = 1031 is the smallest prime divisor congruent to 1 mod 10 of (R^5 - 1)/(R - 1) = 18139194759758381 = 1031 * 17593787351851, where Q = 11 * 211 and R = 5Q.
MATHEMATICA
a={11}; q=1;
For[n=2, n<=6, n++,
q=q*Last[a]; r=5*q;
AppendTo[a, Min[Select[FactorInteger[(r^5-1)/(r-1)][[All, 1]], Mod[#, 10]==1&]]];
];
a (* Robert Price, Jul 14 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Nick Hobson, Nov 18 2006
EXTENSIONS
a(20)..a(34) in b-file from Max Alekseyev, Oct 23 2008
STATUS
approved