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A063640 Primes of form p*q*r + 1, where p, q and r are primes. 4
13, 19, 29, 31, 43, 53, 67, 71, 79, 103, 131, 139, 149, 173, 191, 223, 239, 269, 283, 293, 311, 317, 367, 389, 419, 431, 439, 443, 499, 509, 557, 599, 607, 619, 643, 647, 653, 659, 683, 743, 773, 787, 797, 823, 827, 907, 947, 971, 1031, 1039, 1087, 1091 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also semiprimes of the form (p-1)/2 where p is a prime. - Robert G. Wilson v, Sep 01 2007

LINKS

Harry J. Smith, Table of n, a(n) for n=1,...,1000

MATHEMATICA

Take[ Select[ Union@ Flatten@ Table[ Prime@p*Prime@q*Prime@r + 1, {p, 48}, {q, p}, {r, q}], PrimeQ@ # &], 53] (* Or *)

semiPrimeQ[x_] := Plus @@ Last /@ FactorInteger[x] == 2; Select[Prime@ Range@ 182, semiPrimeQ[(# - 1)/2] &] (* Robert G. Wilson v, Sep 01 2007 *)

2#+1&/@Select[Table[(n-1)/2, {n, Prime[Range[200]]}], PrimeOmega[#]==2&] (* Harvey P. Dale, Oct 11 2018 *)

PROG

(PARI) { n=0; for (m=1, 10^9, p=prime(m); if (bigomega(p - 1) == 3, write("b063640.txt", n++, " ", p); if (n==1000, break)) ) } \\ Harry J. Smith, Aug 26 2009

CROSSREFS

Cf. A014612, A063639.

Sequence in context: A123840 A258589 A103804 * A092104 A281483 A094105

Adjacent sequences:  A063637 A063638 A063639 * A063641 A063642 A063643

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Jul 21 2001

STATUS

approved

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Last modified May 11 12:47 EDT 2021. Contains 343791 sequences. (Running on oeis4.)