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A309743 Numbers k such that 9*10^(2*k) + 9*10^k + 1 are prime. 3
0, 1, 2, 6, 12, 245, 298, 2967, 4321 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..9.

EXAMPLE

           19 is prime. ==> a(1) = 0.

          991 is prime. ==> a(2) = 1.

        90901 is prime. ==> a(3) = 2.

      9009001 = 131 * 68771.

    900090001 = 421 * 2137981.

  90000900001 = 131 * 701 * 980071.

9000009000001 is prime. ==> a(4) = 6.

PROG

(PARI) for(k=0, 1e3, if(ispseudoprime(9*100^k+9*10^k+1), print1(k", ")))

CROSSREFS

Cf. A309739.

Sequence in context: A179201 A105122 A132076 * A291062 A058046 A298410

Adjacent sequences:  A309740 A309741 A309742 * A309744 A309745 A309746

KEYWORD

nonn,more

AUTHOR

Seiichi Manyama, Aug 15 2019

STATUS

approved

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Last modified July 23 11:07 EDT 2021. Contains 346259 sequences. (Running on oeis4.)