A176687 Numbers k such that k^2-1 is the product of 4 distinct primes.

34, 56, 86, 92, 94, 104, 106, 142, 144, 160, 164, 166, 184, 186, 194, 196, 202, 204, 214, 216, 218, 220, 230, 232, 236, 248, 256, 266, 272, 284, 300, 302, 304, 320, 322, 328, 340, 346, 358, 384, 392, 394, 398, 400, 412, 414, 416, 430, 434, 446, 452, 456, 464

Offset: 1

Author

Vladimir Joseph Stephan Orlovsky, Apr 23 2010

Keywords

• nonn

Examples

			34 is in the sequence, because 34^2 - 1 = 1155 = 3 * 5 * 7 * 11, so it's a product of 4 distinct primes.
		

Links

• Daniel Starodubtsev, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A006881, A007304, A014574, A046386, A176686

Programs

Mathematica

Select[Range[7! ],Last/@FactorInteger[ #^2-1]=={1,1,1,1}&]
dp4Q[n_]:=Module[{c=n^2-1},PrimeNu[c]==PrimeOmega[c]==4]; Select[Range[ 500], dp4Q] (* Harvey P. Dale, Dec 31 2013 *)