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A191350
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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.
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2
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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
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2,2
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LINKS
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EXAMPLE
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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.
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PROG
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(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
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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