A100930 Semiprimes of the form (2*p+1)*(p-1)/2, p prime.

22, 115, 517, 6847, 31951, 128701, 516601, 1037851, 2070001, 4156501, 4254937, 6045451, 7945351, 8425957, 8777887, 9137017, 13124317, 14278951, 14460907, 14920837, 24194101, 29146501, 31795501, 47592751, 48758797, 50108701

Offset: 1

Author

Reinhard Zumkeller, Nov 22 2004

Keywords

• nonn

Comments

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

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000
• Eric Weisstein's World of Mathematics, Semiprime
• Eric Weisstein's World of Mathematics, Sophie Germain Prime

Crossrefs

Subsequence of A100929.

Cf. A001358, A005384, A005385.

Programs

Mathematica

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