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 A101221 Least k such that (10^k)*(P(n)#) - 1 is prime with P(i)= i-th prime and P(i)#= i-th primorial. 0
 1, 1, 2, 1, 1, 1, 3, 2, 1, 1, 40, 1, 1, 10, 10, 10, 7, 17, 4, 11, 15, 10, 11, 54, 24, 8, 11, 2, 18, 2, 6, 4, 58, 3, 14, 15, 1, 3, 13, 16, 1, 37, 4, 4, 8, 11, 80, 2, 37, 58, 55, 34, 15, 59, 26, 1, 32, 42, 47, 56, 47, 4, 57, 62, 27, 18, 14, 17, 12, 47, 19, 16, 39, 9, 71, 13, 6, 6, 25, 10, 1, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS EXAMPLE (10^1)*2 -1 = 19 prime so k(1)=1. (10^1)*6 -1 = 59 prime so k(2)=1. (10^2)*30 -1 = 2999 prime so k(3)=2. PROG (PARI) a(n) = {prd = prod(i=1, n, prime(i)); k = 1; while (!isprime(10^k*prd-1), k++); k; } \\ Michel Marcus, Aug 06 2014 CROSSREFS Cf. A002110. Sequence in context: A222580 A284345 A183214 * A086291 A262766 A262747 Adjacent sequences:  A101218 A101219 A101220 * A101222 A101223 A101224 KEYWORD nonn AUTHOR Pierre CAMI, Dec 15 2004 EXTENSIONS Corrected by Michel Marcus, Aug 06 2014 STATUS approved

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Last modified February 23 07:06 EST 2018. Contains 299473 sequences. (Running on oeis4.)