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

1,1

Links

Ray Chandler, Table of n, a(n) for n = 1..10000

Index to sequences related to prime signature

Formula

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

Example

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

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

Crossrefs

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

Sequence in context: A180292 A143928 A356743 * A273459 A092068 A093520

Adjacent sequences: A074170 A074171 A074172 * A074174 A074175 A074176

Keyword

nonn

Author

Amarnath Murthy, Aug 30 2002

Extensions

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

Status

approved