A102961 - OEIS

A102961

Numbers k such that 2*10^k + 8*R_k - 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

1, 2, 7, 28, 73, 295, 494, 598, 2600, 3730, 7549, 15865

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OFFSET

1,2

COMMENTS

Also numbers k such that (26*10^k-53)/9 is prime.

a(13) > 10^5. - Robert Price, Apr 18 2014

LINKS

FORMULA

a(n) = A101970(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[(26*10^k - 53)/9], Print[k]], {k, 1, 10000}]

CROSSREFS

KEYWORD

more,nonn

AUTHOR

EXTENSIONS

Addition of a(12) from Kamada data by Robert Price, Dec 13 2010

0 removed by Georg Fischer, Jan 03 2021

STATUS

approved