A347680 Beginning with 3, least prime > a(n-1) using only digits 2 and 3 such that every concatenation a(1),a(2),... is a palindrome.

3, 23, 3323, 233323, 22223233323233323, 223333322323332323332322223233323233323, 3322233323332323332322223233323233323223333322323332323332322223233323233323

Offset

1,1

Comments

a(11) has 1258 decimal digits.

Links

Chai Wah Wu, Table of n, a(n) for n = 1..10

Example

3, 323, 3233323,... are all palindromes.

Mathematica

a[1]=3; a[n_]:=a[n]=(t=1; While[!IntegerQ[k=Min[FromDigits/@Select[Select[Tuples[{2, 3}, t], PrimeQ@FromDigits@#&], PalindromeQ@FromDigits@Flatten[{IntegerDigits/@Array[a, n-1], #}]&]]]||k<=a[n-1], t++]; k); Array[a, 5] (* Giorgos Kalogeropoulos, Sep 15 2021 *)

Crossrefs

Cf. A002113.

Sequence in context: A210734 A166315 A371346 * A113577 A224700 A352333

Adjacent sequences: A347677 A347678 A347679 * A347681 A347682 A347683

Keyword

nonn,base

Author

N. J. A. Sloane and Chai Wah Wu, Sep 15 2021

Status

approved