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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.
2
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
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
Sequence in context: A304091 A278801 A307720 * A329616 A304795 A036459
KEYWORD
nonn,base
AUTHOR
Vladimir Shevelev, May 31 2011
EXTENSIONS
a(16)-a(91) from Charles R Greathouse IV, Jun 01 2011
STATUS
approved