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A262657 Minimal nested palindromic base-7 primes with seed 1; see Comments. 3
1, 212, 42124, 204212402, 2220421240222, 222204212402222, 2222220421240222222, 12222222042124022222221, 3122222220421240222222213, 331222222204212402222222133, 53312222222042124022222221335, 165331222222204212402222222133561 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Using only base-7 digits 0,1,2,3,4,5,6 let s be a palindrome and put a(1) = s. Let a(2) be the least palindromic prime having s in the middle; for n > 2, let a(n) be the least palindromic prime have a(n-1) in the middle. Then (a(n)) is the sequence of minimal nested palindromic base-7 primes with seed s.

LINKS

Clark Kimberling, Table of n, a(n) for n = 1..300

EXAMPLE

a(3) = 42124 is the least base-7 prime having a(2) = 212 in its middle. Triangular format:

         1

        212

       42124

     204212402

   2220421240222

  222204212402222

2222220421240222222

MATHEMATICA

s = {1}; base = 7; z = 20; Do[NestWhile[# + 1 &, 1, ! PrimeQ[tmp = FromDigits[Join[#, IntegerDigits[Last[s]], Reverse[#]] &[IntegerDigits[#, base]], base]] &];

AppendTo[s, FromDigits[IntegerDigits[tmp, base]]], {z}]; s  (* A262657 *)

Map[FromDigits[ToString[#], base] &, s]  (* A262658 *)

(* Peter J. C. Moses, Sep 01 2015 *)

CROSSREFS

Cf. A261881 (base 10), A262658, A262627.

Sequence in context: A007942 A210257 A239045 * A079794 A197106 A138568

Adjacent sequences:  A262654 A262655 A262656 * A262658 A262659 A262660

KEYWORD

nonn,easy,base

AUTHOR

Clark Kimberling, Oct 27 2015

STATUS

approved

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Last modified May 18 10:28 EDT 2022. Contains 353807 sequences. (Running on oeis4.)