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A153088 Numbers n such that 5*n-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 non-integer 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 by 20, 4 replaced by 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 September 22 09:19 EDT 2017. Contains 292336 sequences.