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A156592 Product p*q of two primes with q = 2*p + 1. 12
10, 21, 55, 253, 1081, 1711, 3403, 5671, 13861, 15931, 25651, 34453, 60031, 64261, 73153, 108811, 114481, 126253, 158203, 171991, 258121, 351541, 371953, 392941, 482653, 518671, 703891, 822403, 853471, 869221, 933661, 1034641, 1104841 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Subsequence of A068443.

Products of Sophie Germain primes p with their corresponding safe primes 2p+1. The smallest prime factor of a(n) is (a(n) - phi(a(n)))/3 and the largest prime factor of a(n) is 2(a(n) - phi(a(n)))/3 + 1. - Wesley Ivan Hurt, Oct 03 2013

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..4000

Math Marathon (MM95) (in Russian) [from Vladimir Joseph Stephan Orlovsky, May 12 2010]

FORMULA

a(n) = A005384(n)*A005385(n).

MATHEMATICA

lst={}; Do[p=Prime[n]; q=2*p+1; If[PrimeQ[q], AppendTo[lst, p*q]], {n, 5!}]; lst (* Vladimir Joseph Stephan Orlovsky, May 12 2010 *)

CROSSREFS

Cf. A005384, A005385. Subset of A001358.

Sequence in context: A048697 A090076 A231966 * A045973 A095679 A095192

Adjacent sequences:  A156589 A156590 A156591 * A156593 A156594 A156595

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Feb 10 2009

STATUS

approved

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Last modified December 7 09:33 EST 2019. Contains 329843 sequences. (Running on oeis4.)