A100930 - OEIS

%I #7 Apr 13 2020 16:13:34

%S 22,115,517,6847,31951,128701,516601,1037851,2070001,4156501,4254937,

%T 6045451,7945351,8425957,8777887,9137017,13124317,14278951,14460907,

%U 14920837,24194101,29146501,31795501,47592751,48758797,50108701

%N Semiprimes of the form (2*p+1)*(p-1)/2, p prime.

%C a(n) = (2*A059455(n)^2 - A059455(n) - 1) / 2.

%H Harvey P. Dale, <a href="/A100930/b100930.txt">Table of n, a(n) for n = 1..1000</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Semiprime.html">Semiprime</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/SophieGermainPrime.html">Sophie Germain Prime</a>

%t Select[Table[((2p+1)(p-1))/2,{p,Prime[Range[2000]]}],PrimeOmega[#]==2&] (* _Harvey P. Dale_, Apr 13 2020 *)

%Y Subsequence of A100929.

%Y Cf. A001358, A005384, A005385.

%K nonn

%O 1,1

%A _Reinhard Zumkeller_, Nov 22 2004