A102954 Numbers n such that 2*10^n + 4*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

3, 9, 15, 21, 27, 87, 180, 1941, 3960, 4995, 8577, 23481, 27855, 80595

Offset

1,1

Comments

Also numbers n such that (22*10^n+23)/9 is prime.

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

Links

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

Makoto Kamada, Prime numbers of the form 244...447.

Index entries for primes involving repunits.

Formula

a(n) = A101959(n) + 1.

Mathematica

Do[ If[ PrimeQ[(22*10^n + 23)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101959.

Sequence in context: A222640 A110108 A162843 * A272749 A273560 A246388

Adjacent sequences: A102951 A102952 A102953 * A102955 A102956 A102957

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 17 2004

Extensions

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

a(14) from Robert Price, Mar 15 2015

Status

approved