A102980 - OEIS

A102980

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

2, 3, 6, 17, 20, 45, 57, 78, 119, 137, 509, 710, 1127, 1518, 1761, 3086, 3147, 9926, 19854, 27842, 46799, 49682, 68718, 100542, 106649, 191073

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OFFSET

1,1

COMMENTS

Also numbers n such that (35*10^n+1)/9 is prime.

LINKS

FORMULA

a(n) = A101847(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[(35*10^n + 1)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

KEYWORD

more,nonn

AUTHOR

EXTENSIONS

Addition of a(19)-a(26) from Kamada data by Robert Price, Dec 08 2010

STATUS

approved