A103062 Numbers n such that 7*10^n + 5*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 1, 3, 237, 243, 351, 967, 1843, 7405, 9633, 59821

Offset

1,3

Comments

Also numbers n such that (68*10^n + 31)/9 is prime.

a(12) > 10^5. - Robert Price, Oct 03 2015

Links

Table of n, a(n) for n=1..11.

Makoto Kamada, Prime numbers of the form 755...559.

Index entries for primes involving repunits.

Formula

a(n) = A101146(n-1) + 1 for n>1.

Example

For n=0, (68*10^n + 31)/9 = 11 which is a prime, so 0 is a term.

Mathematica

Do[ If[ PrimeQ[(68*10^n + 31)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101146.

Sequence in context: A299836 A299725 A278318 * A157723 A342631 A142730

Adjacent sequences: A103059 A103060 A103061 * A103063 A103064 A103065

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(1)=0 inserted and a(11) added by Robert Price, Oct 03 2015

Status

approved