A319858 - OEIS

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

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..100.

EXAMPLE

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.

MATHEMATICA

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

PROG

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

CROSSREFS

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

Sequence in context: A065465 A265308 A375153 * A351210 A199597 A366149

Adjacent sequences: A319855 A319856 A319857 * A319859 A319860 A319861

KEYWORD

nonn,base,easy

AUTHOR

Anton Deynega, Sep 29 2018

STATUS

approved