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A096240 Number of n-digit base-7 deletable primes. 0
3, 7, 21, 59, 184, 534, 1620, 4889, 15607, 50138, 165569, 551580, 1860565, 6345080 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A prime p is a base-b deletable prime if when written in base b it has the property that removing some digit leaves either the empty string or another deletable prime. "Digit" means digit in base b.

Deleting a digit cannot leave any leading zeros in the new string. For example, deleting the 2 in 2003 to obtain 003 is not allowed.

LINKS

Table of n, a(n) for n=1..14.

MATHEMATICA

b = 7; a = {3}; d = {2, 3, 5};

For[n = 2, n <= 7, n++,

  p = Select[Range[b^(n - 1), b^n - 1], PrimeQ[#] &];

  ct = 0;

  For[i = 1, i <= Length[p], i++,

   c = IntegerDigits[p[[i]], b];

   For[j = 1, j <= n, j++,

    t = Delete[c, j];

    If[t[[1]] == 0, Continue[]];

    If[MemberQ[d, FromDigits[t, b]], AppendTo[d, p[[i]]]; ct++;

     Break[]]]];

  AppendTo[a, ct]];

a (* Robert Price, Nov 12 2018 *)

CROSSREFS

Cf. A080608, A080603, A096235-A096246.

Sequence in context: A178718 A244897 A091650 * A182887 A035080 A229188

Adjacent sequences:  A096237 A096238 A096239 * A096241 A096242 A096243

KEYWORD

nonn,base,more

AUTHOR

Michael Kleber, Feb 28 2003

EXTENSIONS

9 more terms from Ryan Propper, Jul 19 2005

STATUS

approved

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Last modified December 7 18:12 EST 2019. Contains 329847 sequences. (Running on oeis4.)