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A077715 a(1) = 7; thereafter a(n) = the smallest prime of the form d0...0a(n-1), where d is a single digit, or 0 if no such prime exists. 3
7, 17, 317, 6317, 26317, 126317, 2126317, 72126317, 372126317, 5372126317, 305372126317, 9305372126317, 409305372126317, 20409305372126317, 100020409305372126317, 9100020409305372126317, 209100020409305372126317, 40209100020409305372126317 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(n) is the smallest prime obtained by prefixing a(n-1) with a number of the form d*10^k where d is a single digit, 0 < d < 10, and k >= 0. Conjecture: d*10^k always exists.

LINKS

Table of n, a(n) for n=1..18.

MAPLE

a:= proc(n) option remember; local k, m, d, p;

      if n=1 then 7 else k:= a(n-1);

        for m from length(k) do

          for d to 9 do p:= k +d*10^m;

            if isprime(p) then return p fi

        od od

      fi

    end:

seq(a(n), n=1..20);  # Alois P. Heinz, Jan 12 2015

CROSSREFS

Cf. A053584, A077713, A077714, A077716.

Sequence in context: A110120 A201305 A053584 * A089563 A159028 A102266

Adjacent sequences:  A077712 A077713 A077714 * A077716 A077717 A077718

KEYWORD

base,nonn

AUTHOR

Amarnath Murthy, Nov 19 2002

EXTENSIONS

More terms from Ray Chandler, Jul 23 2003

Definition clarified by N. J. A. Sloane, Jan 19 2015

STATUS

approved

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Last modified October 21 05:28 EDT 2021. Contains 348141 sequences. (Running on oeis4.)