|
%I #14 Dec 04 2016 19:46:33
%S 7,10,16,17,19,25,27,28,32,34,38,42,43,45,46,47,55,57,59,61,64,66,70,
%T 71,72,77,79,80,88,91,92,93,100,101,102,104,106,107,108,109,110,117,
%U 118,123,124,126,129,132,133,143,145,147,149,150,151,152,154,159
%N Integers of the form (p*q - 1)/2, where p and q are distinct primes.
%C A102770 is subsequence. - _Zak Seidov_, Feb 21 2014
%H Vincenzo Librandi, <a href="/A234093/b234093.txt">Table of n, a(n) for n = 1..1000</a>
%e (3*5 - 1)/2 = 7; (3*7 - 1)/2 = 10.
%t t = Select[Range[1, 7000, 2], Map[Last, FactorInteger[#]] == Table[1, {2}] &]; Take[(t - 1)/2, 120] (* A234093 *)
%t v = Flatten[Position[PrimeQ[(t - 1)/2], True]] ; w = Table[t[[v[[n]]]], {n, 1, Length[v]}] (* A233561 *)
%t (w - 1)/2 (* A234095 *) (* _Peter J. C. Moses_, Dec 23 2013 *)
%t With[{nn=60},Take[Union[Select[(Times@@#-1)/2&/@Subsets[Prime[ Range[ nn]],{2}],IntegerQ]],nn]] (* _Harvey P. Dale_, Mar 08 2015 *)
%Y Cf. A102770, A233561, A234095, A234096.
%K nonn,easy
%O 1,1
%A _Clark Kimberling_, Dec 27 2013
|
