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A046953 Numbers k such that 6*k - 1 is composite. 12
6, 11, 13, 16, 20, 21, 24, 26, 27, 31, 34, 35, 36, 37, 41, 46, 48, 50, 51, 54, 55, 56, 57, 61, 62, 63, 66, 68, 69, 71, 73, 76, 79, 81, 83, 86, 88, 89, 90, 91, 92, 96, 97, 101, 102, 104, 105, 106, 111, 112, 115, 116, 118, 119, 121, 122, 123, 125, 126, 128 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

These numbers can be written as 6*x*y + x - y for x > 0, y > 0. - Ron R Spencer, Aug 01 2016

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

FORMULA

a(n) ~ n. - Charles R Greathouse IV, Aug 01 2016

EXAMPLE

a(1)=6 because 6*6 - 1 = 35, which is composite.

MAPLE

remove(k-> isprime(6*k-1), [$1..130])[]; # Muniru A Asiru, Feb 22 2019

MATHEMATICA

Select[Range[200], !PrimeQ[6#-1]&] (* Vladimir Joseph Stephan Orlovsky, Feb 25 2011 *)

PROG

(Haskell)

a046953 n = a046953_list !! (n-1)

a046953_list = map (`div` 6) $

   filter ((== 0) . a010051' . subtract 1) [6, 12..]

-- Reinhard Zumkeller, Jul 13 2014

(PARI) is(n)=!isprime(6*n-1) \\ Charles R Greathouse IV, Aug 01 2016

(MAGMA) [n: n in [1..200] | not IsPrime(6*n-1)]; // G. C. Greubel, Feb 21 2019

(Sage) [n for n in (1..200) if not is_prime(6*n-1)] # G. C. Greubel, Feb 21 2019

(GAP) Filtered([1..200], k-> not IsPrime(6*k-1)) # G. C. Greubel, Feb 21 2019

CROSSREFS

Cf. A046954, A008588, A016969, subsequence of A067611.

Cf. A024898 (complement).

Sequence in context: A004471 A175021 A315367 * A121765 A315368 A315369

Adjacent sequences:  A046950 A046951 A046952 * A046954 A046955 A046956

KEYWORD

nonn

AUTHOR

Felice Russo

STATUS

approved

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Last modified April 10 15:47 EDT 2021. Contains 342845 sequences. (Running on oeis4.)