A103015 - OEIS

A103015

Numbers n such that 5*10^n + 4*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

2, 6, 8, 18, 53, 68, 242, 276, 320, 564, 620, 1782, 2340, 2454, 5765, 15530, 15605, 22938

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OFFSET

1,1

COMMENTS

Also numbers n such that (49*10^n+23)/9 is prime.

a(19) > 10^5. - Robert Price, Jul 29 2015

LINKS

FORMULA

a(n) = A101580(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[(49*10^n + 23)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

KEYWORD

more,nonn

AUTHOR

EXTENSIONS

a(16)-a(18) from Kamada data by Robert Price, Dec 14 2010

STATUS

approved