A102952 Numbers k such that 2*10^k + 4*R_k - 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

2, 3, 6, 11, 30, 128, 183, 375, 2159, 2568, 3369, 24989, 38810, 59558, 74874

Offset

1,1

Comments

Also numbers k such that (22*10^k - 31)/9 is prime.

a(16) > 10^5. - Robert Price, Apr 11 2015

Links

Table of n, a(n) for n=1..15.

Makoto Kamada, Prime numbers of the form 244...441.

Index entries for primes involving repunits.

Formula

a(n) = A101957(n) + 1.

Mathematica

Do[ If[ PrimeQ[(22*10^n - 31)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101957.

Sequence in context: A324768 A086209 A022490 * A369223 A065653 A275783

Adjacent sequences: A102949 A102950 A102951 * A102953 A102954 A102955

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 17 2004

Extensions

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

a(13) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

a(14)-a(15) from Robert Price, Apr 11 2015

Status

approved