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A153343 Numbers k such that 5*k + 4 is not prime. 7
0, 1, 2, 4, 6, 7, 8, 9, 10, 12, 13, 14, 16, 18, 19, 20, 22, 23, 24, 25, 26, 28, 30, 31, 32, 33, 34, 36, 37, 38, 40, 41, 42, 43, 44, 46, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 70, 72, 73, 74, 76, 78, 79, 80, 82, 84, 85, 86, 88 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Apart from a(0) = 0 and a(1) = 1 this sequence comprises those numbers k such that (5*k)!/(5*k + 4) is an integer. - Peter Bala, Jan 25 2017

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

EXAMPLE

Distribution of the odd terms in the following triangular array:

   1;

   *,   *;

   *,   *,   9;

   *,   *,   *,   *;

   *,   *,   *,  19,   *;

   7,   *,   *,   *,   *,  33;

   *,   *,   *,   *,   *,   *,   *;

   *,   *,  23,   *,   *,   *,   *,  57;

   *,   *,   *,   *,  41,   *,   *,   *,   *;

   *,   *,   *,  37,   *,   *,   *,   *,  79,   *;

  13,   *,   *,   *,   *,  59,   *,   *,   *,   *,  105;

etc., where * marks the noninteger values of (4*h*k + 2*k + 2*h - 3)/5 with h >= k >= 1. - Vincenzo Librandi, Jan 17 2013

MAPLE

# produces the sequence apart from the initial terms 0 and 1

for n from 0 to 100 do

if irem(factorial(5*n), 5*n+4) = 0 then print(n); end if;

end do: # Peter Bala, Jan 25 2017

MATHEMATICA

Select[Range[0, 200], !PrimeQ[5*# + 4]&] (* Vincenzo Librandi, Jan 12 2013 *)

PROG

(MAGMA) [n: n in [0..150] | not IsPrime(5*n + 4)]; // Vincenzo Librandi, Jan 12 2013

CROSSREFS

Cf. A024897, A014076, A153170, A045751, A095277, A153088, A153343.

Sequence in context: A155939 A114145 A153351 * A136499 A047513 A039068

Adjacent sequences:  A153340 A153341 A153342 * A153344 A153345 A153346

KEYWORD

nonn,easy

AUTHOR

Vincenzo Librandi, Dec 24 2008

EXTENSIONS

Erroneous comment deleted by N. J. A. Sloane, Jun 23 2010

0 added by Arkadiusz Wesolowski, Aug 03 2011

STATUS

approved

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Last modified April 8 02:27 EDT 2020. Contains 333312 sequences. (Running on oeis4.)