A102958 Numbers n such that 2*10^n + 7*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 1, 4, 10, 165, 228, 384, 2890, 3445, 10069, 17356, 25804, 29052, 29082

Offset

1,3

Comments

Also numbers n such that (25*10^n-43)/9 is prime.

a(15) > 10^5. - Robert Price, Mar 01 2015

Links

Table of n, a(n) for n=1..14.

Makoto Kamada, Prime numbers of the form 277...773.

Index entries for primes involving repunits.

Formula

a(n) = A101967(n-1) + 1.

Mathematica

Do[ If[ PrimeQ[(25*10^n - 43)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101967.

Sequence in context: A273517 A370687 A003086 * A321795 A220197 A299880

Adjacent sequences: A102955 A102956 A102957 * A102959 A102960 A102961

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 17 2004

Extensions

Addition of a(10)-a(14) from Kamada data by Robert Price, Dec 12 2010

Status

approved