A098960 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A098960

Numbers k such that 2*10^k + 7*R_k - 6 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

1

2, 6, 33, 69, 150, 936, 3135, 5838, 6990, 20786, 57138

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

Also numbers k such that (25*10^k - 61)/9 is prime.

a(12) > 10^5. - Robert Price, Feb 27 2015

LINKS

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

Makoto Kamada, Prime numbers of the form 277...771.

Index entries for primes involving repunits.

FORMULA

a(n) = A101966(n) + 1.

EXAMPLE

For n = 2 and 6, we get 271 and 2777771 which are primes.

MATHEMATICA

Do[ If[ PrimeQ[(25*10^n - 61)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

Cf. A002275, A101966.

Sequence in context: A372902 A083666 A083126 * A162429 A279461 A243324

Adjacent sequences: A098957 A098958 A098959 * A098961 A098962 A098963

KEYWORD

more,nonn

AUTHOR

Julien Peter Benney (jpbenney(AT)ftml.net), Oct 22 2004

EXTENSIONS

a(6) from Ray Chandler, Nov 04 2004

a(7), a(8) & a(9) from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Nov 03 2004

Addition of a(10) from Kamada data by Robert Price, Dec 13 2010

a(11) from Robert Price, Feb 27 2015

STATUS

approved