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%I A176686 #8 Jul 24 2016 16:51:25
%S A176686 14,16,20,22,32,36,38,40,52,54,58,66,68,70,78,84,88,90,96,110,112,114,
%T A176686 128,130,132,140,156,158,162,178,182,200,210,212,222,234,238,250,252,
%U A176686 258,264,268,292,294,306,308,310,318,330,336,338,354,366,372,378,380
%N A176686 Numbers n such that n^2-1 are products of 3 distinct primes.
%C A176686 14^2-1=195=3*5*13, 16^2-1=255=3*5*17, 20^2-1=399=3*7*19.
%C A176686 All terms are even since n^2-1 for n odd is a multiple of 4.  If m is a term, then (m-1, m+1) contains one prime and one nonsquare semiprime. - _Chai Wah Wu_, Mar 28 2016
%H A176686 Chai Wah Wu, <a href="/A176686/b176686.txt">Table of n, a(n) for n = 1..10000</a>
%t A176686 Select[Range[6! ],Last/@FactorInteger[ #^2-1]=={1,1,1}&]
%t A176686 Sqrt[#+1]&/@Select[Sort[Times@@@Subsets[Prime[Range[100]],{3}]], IntegerQ[ Sqrt[#+1]]&] (* _Harvey P. Dale_, Jul 24 2016 *)
%Y A176686 Cf. A006881, A007304, A014574, A046386
%K A176686 nonn
%O A176686 1,1
%A A176686 _Vladimir Joseph Stephan Orlovsky_, Apr 23 2010

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