OFFSET
1,1
COMMENTS
According to the link, there are only 18 "unique primes" below 10^50. The first four terms above are each unique primes, of periods 12, 24, 36 and 48, respectively, according to Caldwell and the cross-referenced sequences. These are precisely the only unique primes (less than 10^50 at least) with this type of digit pattern: m 9's, m-1 0's and 1, in that order. (Also a(10) is a unique prime of period 120.)
LINKS
Max Alekseyev, Table of n, a(n) for n = 1..87 (terms n=1..51 from Ray Chandler, n=52..81 from Daniel Suteu)
C. K. Caldwell, Unique Primes
Makoto Kamada, Factorizations of 100...001.
FORMULA
EXAMPLE
10^(6*4)+1 = 17 * 5882353 * 9999999900000001, so a(4) = 9999999900000001, the largest prime factor.
PROG
(PARI) for(n=1, 12, v=factor(10^(6*n)+1); print1(v[matsize(v)[1], 1], ", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Rick L. Shepherd, Jul 25 2002
STATUS
approved