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

1,1

Links

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

Example

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

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 *)

Crossrefs

Cf. A006881, A007304, A014574, A046386, A176686

Sequence in context: A227304 A055574 A294173 * A224896 A103558 A103686

Adjacent sequences: A176684 A176685 A176686 * A176688 A176689 A176690

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Apr 23 2010

Status

approved