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A153329 Numbers n such that 5*n+1 is not prime. 7
0, 1, 3, 4, 5, 7, 9, 10, 11, 13, 15, 16, 17, 18, 19, 21, 22, 23, 24, 25, 27, 28, 29, 31, 32, 33, 34, 35, 37, 39, 40, 41, 43, 44, 45, 46, 47, 49, 51, 52, 53, 55, 57, 58, 59, 60, 61, 63, 64, 65, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 81, 82, 83, 85, 87 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Numbers n such that (5*n)!/(5*n + 1) is an integer. - Peter Bala, Jan 25 2017

LINKS

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

EXAMPLE

Distribution of the even terms in the following triangular array:

*;

*,*;

4,*,*;

*,*,*,16;

*,*,*,*,24;

*,*,18,*,*,*;

*,*,*,*,*,*,*;

10,*,*,*,*,44,*,*;

*,*,*,34,*,*,*,*,72;

*.*,*,*,46,*,*,*,*,88;

*,*,32,*,*,*,*,78,*,*,*; etc.

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

MAPLE

for n from 0 to 100 do

if irem(factorial(5*n), 5*n+1) = 0 then print(n); end if;

end do:

# - Peter Bala, Jan 25 2017

MATHEMATICA

Select[Range[0, 200], !PrimeQ[5*# + 1]&] (* Vincenzo Librandi, Jan 12 2013 *)

PROG

(MAGMA) [n: n in [0..150] | not IsPrime(5*n + 1)]; // Vincenzo Librandi, Jan 12 2013

CROSSREFS

Cf. A024894, A014076, A153170, A045751, A095277, A153088, A153343.

Sequence in context: A275319 A276155 A273670 * A213637 A047251 A258932

Adjacent sequences:  A153326 A153327 A153328 * A153330 A153331 A153332

KEYWORD

nonn,easy

AUTHOR

Vincenzo Librandi, Dec 23 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 March 28 19:06 EDT 2017. Contains 284246 sequences.