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%I #12 Feb 28 2020 10:20:19
%S 34,56,86,92,94,104,106,142,144,160,164,166,184,186,194,196,202,204,
%T 214,216,218,220,230,232,236,248,256,266,272,284,300,302,304,320,322,
%U 328,340,346,358,384,392,394,398,400,412,414,416,430,434,446,452,456,464
%N Numbers k such that k^2-1 is the product of 4 distinct primes.
%H Daniel Starodubtsev, <a href="/A176687/b176687.txt">Table of n, a(n) for n = 1..10000</a>
%e 34 is in the sequence, because 34^2 - 1 = 1155 = 3 * 5 * 7 * 11, so it's a product of 4 distinct primes.
%t Select[Range[7! ],Last/@FactorInteger[ #^2-1]=={1,1,1,1}&]
%t dp4Q[n_]:=Module[{c=n^2-1},PrimeNu[c]==PrimeOmega[c]==4]; Select[Range[ 500], dp4Q] (* _Harvey P. Dale_, Dec 31 2013 *)
%Y Cf. A006881, A007304, A014574, A046386, A176686
%K nonn
%O 1,1
%A _Vladimir Joseph Stephan Orlovsky_, Apr 23 2010
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