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A055558 Primes of the form 1999...999. 11
19, 199, 1999, 199999, 19999999, 199999999999999999999999999, 1999999999999999999999999999, 199999999999999999999999999999999999999999999999999999 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..8.

FORMULA

Primes of the form 2*10^n - 1.

EXAMPLE

2*10^n - 1 is prime for {1,2,3,5,7,26,27,53,147,236,248,386,401}; in each of these numbers, the digit '9' appears n times.

PROG

(PARI) for(n=1, 99, if(ispseudoprime(t=2*10^n-1), print1(t", "))) \\ Charles R Greathouse IV, Dec 10 2013

CROSSREFS

Subsequence of A090149.

Cf. A002957, A051200.

Sequence in context: A067272 A065582 A241021 * A160452 A113596 A155670

Adjacent sequences:  A055555 A055556 A055557 * A055559 A055560 A055561

KEYWORD

base,nonn

AUTHOR

Labos Elemer, Jul 10 2000

STATUS

approved

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Last modified April 19 16:18 EDT 2019. Contains 322282 sequences. (Running on oeis4.)