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

Author

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

Keywords

• nonn
• base

Comments

a(11) has 1258 decimal digits.

Examples

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

Links

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

Crossrefs

Cf. A002113.

Programs

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 *)