A074173 Numbers n such that n and n+2 are of the form p^2*q where p and q are distinct primes.

18, 50, 242, 423, 475, 603, 637, 722, 845, 925, 1682, 1773, 2007, 2523, 2525, 2527, 3175, 3177, 4203, 4475, 4525, 4923, 5823, 6725, 6811, 6962, 7299, 7442, 7675, 8425, 8957, 8973, 9457, 9925, 10051, 10082, 10467, 11673, 11709, 12427, 12482, 12591

Offset: 1

Author

Amarnath Murthy, Aug 30 2002

Keywords

• nonn

Examples

			18 is a member as 18 = 3^2*2 and 20 = 2^2*5.
		

Links

• Ray Chandler, Table of n, a(n) for n = 1..10000
• Index to sequences related to prime signature

Crossrefs

Cf. A048161, A054753, A074172, A074174, A308735, A308736.

Programs

Mathematica

lst={}; Do[f1=FactorInteger[n]; If[Sort[Transpose[f1][[2]]]=={1, 2}, f2=FactorInteger[n+2]; If[Sort[Transpose[f2][[2]]]=={1, 2}, AppendTo[lst, n]]], {n, 3, 10000}]; lst

Formula

Even terms in sequence are 2*A048161(n)^2. - Ray Chandler, Jun 24 2019

Extensions

More terms from T. D. Noe, Oct 04 2004