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 60th year, we have over 367,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A241264 Numbers k such that 2*k^2 + 2*k - 41 is not a prime. 1
 4, 13, 20, 24, 26, 30, 31, 32, 35, 36, 37, 38, 40, 41, 43, 47, 49, 51, 54, 55, 60, 62, 63, 64, 67, 70, 71, 72, 73, 75, 76, 78, 79, 81, 82, 84, 85, 88, 89, 92, 94, 97, 98, 100, 102, 105, 108, 109, 111, 112, 113, 114, 115, 117, 118, 119, 120, 122, 123, 124, 125 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..5000 EXAMPLE 13 is in this sequence because 2*13^2 + 2*13 - 41 = 323 = 17*19. MATHEMATICA Select[Range[4, 200], ! PrimeQ[2 #^2 + 2 # - 41] &] PROG (Magma) [n: n in [1..150] | not IsPrime(2*n^2+2*n-41)]; CROSSREFS Complement of A155771. Sequence in context: A141491 A292363 A119048 * A066993 A297884 A298289 Adjacent sequences: A241261 A241262 A241263 * A241265 A241266 A241267 KEYWORD nonn,easy AUTHOR Vincenzo Librandi, Apr 20 2014 STATUS approved

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

Last modified December 7 18:28 EST 2023. Contains 367660 sequences. (Running on oeis4.)