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A102707 a(n) = least k such that k*(10^n) -1 or +1 is prime. 1
1, 1, 1, 2, 5, 2, 3, 2, 6, 6, 3, 11, 18, 4, 5, 6, 13, 11, 15, 3, 6, 14, 6, 6, 61, 8, 2, 2, 3, 9, 48, 48, 21, 15, 6, 30, 3, 9, 6, 18, 6, 33, 30, 3, 60, 6, 24, 33, 33, 8, 71, 31, 11, 2, 5, 3, 24, 9, 16, 39, 19, 6, 9, 53, 60, 6, 26, 3, 16, 23, 17, 19, 44, 6, 131, 56, 8, 26, 9, 42, 12, 3, 24, 41 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Pierre CAMI, Table of n, a(n) for n = 0..999

EXAMPLE

for n=0 1*(10^0)+1=2 prime so a(0)=1

for n=1 1*(10^1)+1=11 prime so a(1)=1

for n=2 1*(10^2)+1=101 prime so a(2)=1

for n=3 2*(10^3)-1=1999 prime so a(3)=2

CROSSREFS

Sequence in context: A100955 A049413 A300691 * A134486 A088006 A078311

Adjacent sequences:  A102704 A102705 A102706 * A102708 A102709 A102710

KEYWORD

nonn

AUTHOR

Pierre CAMI, Feb 05 2005

EXTENSIONS

Initial term of b-file corrected by N. J. A. Sloane, Aug 31 2009

STATUS

approved

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Last modified October 21 22:47 EDT 2019. Contains 328315 sequences. (Running on oeis4.)