%I #12 Nov 14 2018 02:07:04

%S 3,7,21,59,184,534,1620,4889,15607,50138,165569,551580,1860565,6345080

%N Number of n-digit base-7 deletable primes.

%C 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.

%C 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.

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

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

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

%t ct = 0;

%t For[i = 1, i <= Length[p], i++,

%t c = IntegerDigits[p[[i]], b];

%t For[j = 1, j <= n, j++,

%t t = Delete[c, j];

%t If[t[[1]] == 0, Continue[]];

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

%t Break[]]]];

%t AppendTo[a, ct]];

%t a (* _Robert Price_, Nov 12 2018 *)

%Y Cf. A080608, A080603, A096235-A096246.

%K nonn,base,more

%O 1,1

%A _Michael Kleber_, Feb 28 2003

%E 9 more terms from _Ryan Propper_, Jul 19 2005