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A176687
Numbers k such that k^2-1 is the product of 4 distinct primes.
2
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
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
KEYWORD
nonn
AUTHOR
STATUS
approved