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 A153088 Numbers k such that 5*k - 1 is not prime. 8
 1, 2, 3, 5, 7, 8, 9, 10, 11, 13, 14, 15, 17, 19, 20, 21, 23, 24, 25, 26, 27, 29, 31, 32, 33, 34, 35, 37, 38, 39, 41, 42, 43, 44, 45, 47, 49, 50, 51, 52, 53, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 71, 73, 74, 75, 77, 79, 80, 81, 83, 85, 86, 87, 89, 91, 92, 93 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 FORMULA a(n) = A153343(n) + 1. - Peter Bala, Jan 25 2017 EXAMPLE Distribution of the even terms in the following triangular array:    2;    *,   *;    *,   *,  10;    *,   *,   *,   *;    *,   *,   *,  20,   *;    8,   *,   *,   *,   *,  34;    *,   *,   *,   *,   *,   *,   *;    *,   *,  24,   *,   *,   *,   *,  58;    *,   *,   *,   *,  42,   *,   *,   *,   *;    *,   *,   *,  38,   *,   *,   *,   *,  80,   *;   14,   *,   *,   *,   *,  60,   *,   *,   *,   *, 106; etc., where * marks the noninteger values of (4*h*k + 2*k + 2*h + 2)/5 with h >= k >= 1. - Vincenzo Librandi, Jan 15 2013 MAPLE # produces the sequence apart from the initial terms 1 and 2 for n from 0 to 100 do   if irem(factorial(5*n), 5*n+4) = 0 then print(n+1); end if; end do: # Peter Bala, Jan 25 2017 MATHEMATICA Select[Range[1, 200], !PrimeQ[5 # - 1] &] (* Vincenzo Librandi, Oct 11 2012 *) PROG (MAGMA) [n: n in [1..100] | not IsPrime(5*n-1)]; // Vincenzo Librandi, Oct 11 2012 CROSSREFS Cf. A153355, A014076, A153170, A045751, A095277, A153329, A153343. Sequence in context: A039142 A039103 A228082 * A162535 A279814 A047490 Adjacent sequences:  A153085 A153086 A153087 * A153089 A153090 A153091 KEYWORD nonn,easy AUTHOR Vincenzo Librandi, Jan 03 2009 EXTENSIONS First 29 replaced with 20, 4 replaced with 44, extended by R. J. Mathar, Jan 05 2009 Erroneous comment deleted by N. J. A. Sloane, Jun 23 2010 STATUS approved

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Last modified June 18 15:25 EDT 2021. Contains 345120 sequences. (Running on oeis4.)