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Table of n, a(n) for n=1..26.
a(4)=4 because 609*10^4-1 = 6089999, a prime.
(PARI) is(n)=ispseudoprime(609*10^n-1) \\ Charles R Greathouse IV, Jun 13 2017
Sequence in context: A023788 A032989 A322570 * A177958 A032941 A273733
Adjacent sequences: A108317 A108318 A108319 * A108321 A108322 A108323
Jason Earls, Jun 30 2005