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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

Table of n, a(n) for n=1..82.

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: A316978 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 October 17 16:18 EDT 2018. Contains 316285 sequences. (Running on oeis4.)