A103087 - OEIS

A103087

Numbers k such that 8*10^k + 6*R_k - 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

0, 1, 2, 3, 13, 19, 62, 80, 126, 168, 195, 309, 410, 481, 608, 741, 879, 1176, 2688, 6236, 16294, 17317, 31574, 34861, 35392, 48726

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OFFSET

1,3

COMMENTS

Also numbers k such that (26*10^k-11)/3 is prime.

a(27) > 10^5. - Robert Price, Oct 25 2015

LINKS

FORMULA

a(n) = A101074(n-1) + 1, for n>1.

MATHEMATICA

Do[ If[ PrimeQ[(26*10^n - 11)/3], Print[n]], {n, 0, 10000}]

CROSSREFS

KEYWORD

more,nonn

AUTHOR

EXTENSIONS

a(21)-a(22) from Kamada data by Robert Price, Dec 14 2010

a(23)-a(26) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

Inserted a(1)=0 by Robert Price, Oct 25 2015

STATUS

approved