login
A102947
Numbers n such that 2*10^n-3 is prime.
2
1, 2, 3, 4, 13, 14, 76, 237, 872, 988, 1280, 1370, 2686, 3612, 4051, 4645, 9162, 10856, 25959, 64882, 144220, 153746, 185930
OFFSET
1,2
COMMENTS
Numbers n such that 10^n + 8*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
a(21) > 10^5. - Robert Price, Nov 16 2014
a(24) > 2*10^5. - Robert Price, Jul 11 2015
FORMULA
a(n) = A102034(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[2*10^n - 3], Print[n]], {n, 0, 10000}]
PROG
(PARI) is(n)=ispseudoprime(2*10^n-3) \\ Charles R Greathouse IV, Jun 06 2017
CROSSREFS
Cf. A102034.
Sequence in context: A325709 A338478 A126129 * A281512 A295396 A236440
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Dec 16 2004
EXTENSIONS
Addition of a(18)-a(20) from Kamada data by Robert Price, Dec 09 2010
a(21)-a(23) from Robert Price, Jul 11 2015
STATUS
approved