A319858 a(n) is the number of values of m in the interval [2,10] such that the base-m expansion of n, interpreted as a base-10 number, yields a prime.

0, 8, 8, 1, 7, 1, 5, 2, 2, 3, 3, 1, 3, 0, 2, 2, 3, 0, 4, 0, 2, 2, 4, 0, 2, 1, 1, 2, 3, 0, 3, 0, 3, 2, 1, 0, 4, 1, 3, 0, 2, 0, 5, 0, 1, 1, 3, 1, 1, 1, 0, 1, 2, 0, 4, 1, 1, 1, 3, 0, 3, 0, 1, 1, 1, 1, 4, 1, 0, 0, 5, 0, 2, 0, 2, 0, 1, 0, 4, 0, 1, 1, 3, 1, 1, 0, 2, 1, 3, 0, 2, 0, 2, 2, 1, 0, 3, 0, 0, 0

Offset: 1

Author

Anton Deynega, Sep 29 2018

Keywords

• nonn
• base
• easy

Examples

			a(31)=3 because 31 yields primes for 3 bases in [2,10]:  31 = 11111_2 = 1011_3 = 133_4 = 111_5 = 51_6 = 43_7 = 37_8 = 34_9 = 31_10, and of the decimal numbers 11111, 1011, 133, 111, 51, 43, 37, 34, and 31, the 3 primes are 43, 37, and 31.
		

Crossrefs

Cf. A052026 (where a(n) is 0).

Programs

Mathematica

Array[Count[FromDigits /@ IntegerDigits[#, Range[2, 10]], ?PrimeQ] &, 105] (* _Michael De Vlieger, Oct 11 2018 *)

PARI

a(n) = sum(b=2, 10, isprime(fromdigits(digits(n, b), 10))); \\ Michel Marcus, Sep 30 2018