A075240 Smallest prime whose base-n reversal is not a prime.

2, 3, 11, 5, 13, 7, 11, 29, 19, 11, 19, 13, 29, 23, 19, 17, 23, 19, 31, 29, 29, 23, 29, 37, 37, 29, 31, 29, 43, 31, 37, 37, 59, 59, 43, 37, 41, 59, 43, 41, 59, 43, 47, 47, 53, 47, 59, 61, 59, 61, 59, 53, 67, 59, 59, 59, 61, 59, 73, 61, 71, 67, 79, 71, 89, 67, 71, 101, 89

Offset: 2

Author

Robert G. Wilson v, Sep 09 2002

Keywords

• base
• easy
• nonn

Comments

All primes show up in the sequence eventually.

Examples

			11_10 = 23_4, reverse(23) = 32, 32_4 = 14_10, so a(4) = 11 since this does not work for smaller primes.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 2..10000

Crossrefs

Cf. A075241, A075242.

Programs

Mathematica

a = {}; Do[k = 1; While[ PrimeQ[ FromDigits[ Reverse[ IntegerDigits[ Prime[k], n]], n]], k++ ]; a = Append[a, Prime[k]], {n, 2, 70}]; a

PARI

a(n) = my(p=2); while (isprime(fromdigits(Vecrev(digits(p, n)), n)), p = nextprime(p+1)); p; \\ Michel Marcus, Mar 28 2021