This site is supported by donations to The OEIS Foundation.

Annual Appeal: Please make a donation (tax deductible in USA) to keep the OEIS running. Over 4500 articles have referenced us, often saying "we would not have discovered this result without the OEIS".

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A098960 Numbers n such that 2*10^n + 7*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 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 n such that (25*10^n-61)/9 is prime. a(12) > 10^5. - Robert Price, Feb 27 2015 LINKS Makoto Kamada, Prime numbers of the form 277...771. 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: A213435 A083666 A083126 * A162429 A243324 A018952 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .