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
KEYWORD
nonn
AUTHOR
Vladimir Joseph Stephan Orlovsky, Apr 23 2010
STATUS
approved