A191350 - OEIS

A191350

The number of bases not exceeding n+1 in which the expansion of n (i) has only digits <=9 and (ii) represents a prime if digits are concatenated/reinterpreted as decimals.

1, 2, 1, 3, 1, 3, 2, 2, 3, 3, 2, 4, 2, 4, 4, 5, 3, 7, 4, 6, 6, 8, 4, 7, 5, 6, 6, 8, 4, 9, 4, 9, 7, 7, 4, 11, 5, 9, 6, 8, 4, 13, 4, 8, 7, 10, 5, 10, 5, 8, 7, 9, 4, 14, 5, 8, 8, 11, 4, 12, 4, 10, 8, 8, 5, 15, 6, 8, 6, 13, 4, 14, 5, 10, 6, 8, 6, 17, 5, 8, 7, 12, 6, 13, 5, 11, 8, 11, 4, 15, 5

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OFFSET

2,2

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 2..10000

EXAMPLE

In bases 6, 8, 12 and 14 the digits of n=15 are 15_6=23, 15_8=17, 15_12=13, and 15_14=11. Since in other bases<=16 the expansions of 15 converted to decimal are not primes, a(15)=4.

PROG

(PARI) a(n)=my(m, t, k, i); sum(b=2, n+1, k=n; m=0; i=0; while(k, t=k%b; if(t>9, m=0; break); m+=10^i*t; i++; k\=b); isprime(m)) \\ Charles R Greathouse IV, Jun 01 2011

CROSSREFS

Cf. A191291, A191322.

Sequence in context: A304091 A278801 A307720 * A329616 A304795 A036459

Adjacent sequences: A191347 A191348 A191349 * A191351 A191352 A191353

KEYWORD

nonn,base

AUTHOR

Vladimir Shevelev, May 31 2011

EXTENSIONS

a(16)-a(91) from Charles R Greathouse IV, Jun 01 2011

STATUS

approved