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A112775 Numbers n such that 6n+1 is semiprime. 4
4, 8, 9, 14, 15, 19, 20, 22, 24, 28, 31, 34, 36, 39, 41, 42, 43, 44, 48, 49, 50, 53, 59, 60, 65, 67, 69, 71, 74, 75, 78, 80, 82, 84, 85, 86, 88, 89, 92, 93, 94, 97, 98, 108, 109, 111, 113, 114, 116, 117, 120, 124, 127, 130, 132, 133, 136, 139, 140, 144, 145, 148, 149 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Resulting semiprimes in A112771.

LINKS

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

FORMULA

a(n) = (A112771(n) - 1)/6.

MATHEMATICA

Select[Range[200], Plus@@Last/@FactorInteger[6#+1]==2&] (* Vincenzo Librandi, Sep 22 2012 *)

PROG

(MAGMA) IsSemiprime:=func<n | &+[k[2]: k in Factorization(n)] eq 2>; [n: n in [2..150] | IsSemiprime(6*n+1)]; // Vincenzo Librandi, Sep 22 2012

CROSSREFS

Sequence in context: A060299 A120512 A046954 * A107747 A121763 A110087

Adjacent sequences:  A112772 A112773 A112774 * A112776 A112777 A112778

KEYWORD

easy,nonn

AUTHOR

Jonathan Vos Post and Ray Chandler, Oct 15 2005

STATUS

approved

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Last modified January 17 15:12 EST 2020. Contains 330958 sequences. (Running on oeis4.)