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A099017
Numbers k such that 4*10^k + 6*R_k + 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
2
0, 1, 2, 6, 10, 12, 13, 22, 32, 46, 61, 68, 90, 110, 652, 1608, 1904, 2003, 3038, 3086, 9580, 9698, 10639, 14461
OFFSET
1,3
COMMENTS
Also numbers k such that (14*10^k + 1)/3 is prime.
a(25) > 2*10^5. - Robert Price, Jul 11 2015
FORMULA
a(n) = A101731(n-1) + 1, for n>1.
EXAMPLE
n = 1, 2, 6 are members since 47, 467, 4666667 are primes.
MATHEMATICA
Do[ If[ PrimeQ[(14*10^n + 1)/3], Print[n]], {n, 0, 10000}] (* Robert G. Wilson v, Jan 17 2005 *)
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Julien Peter Benney (jpbenney(AT)ftml.net), Nov 13 2004
EXTENSIONS
a(15)-a(22) from Robert G. Wilson v, Jan 17 2005
a(23)-a(24) from Kamada data by Robert Price, Dec 08 2010
Prepended a(1)=0 by Robert Price, Jul 11 2015
STATUS
approved