|
%I #10 Apr 06 2015 06:11:46
%S 4,14,39,46,55,94,155,158,183,203,291,295,299,323,334,446,579,583,695,
%T 718,799,878,943,955,959,979,1191,1255,1411,1454,1678,1703,2019,2059,
%U 2159,2174,2219,2395,2419,2446,2491,2734,2855,3043,3063,3443,3459,3503,3694
%N Product of two primes whose sum is a perfect square.
%H Reinhard Zumkeller, <a href="/A141755/b141755.txt">Table of n, a(n) for n = 1..1000</a>
%t Take[ Sort[ Times @@@ Select[ Subsets[ Array[ Prime, 290], {2}], IntegerQ[ Sqrt[ #[[2]] + #[[1]]]] &]], 48]
%t nn=4000; fQ[n_] := Module[{p, e}, If[n < 2, False, {p, e} = Transpose[FactorInteger[n]]; If[Total[e] != 2, False, IntegerQ[Sqrt[Total[p*e]]]]]]; Select[Range[nn], fQ] (* _T. D. Noe_, Mar 22 2012 *)
%o (Haskell)
%o a141755 n = a141755_list !! (n-1)
%o a141755_list = filter f a001358_list where
%o f x = a010052' (spf + x `div` spf) == 1 where spf = a020639 x
%o -- _Reinhard Zumkeller_, Apr 06 2015
%Y Cf. A000040, A000290, A143416.
%Y Cf. A001358, A020639, A010052.
%K nonn
%O 1,1
%A David Spector (spectord(AT)ccsu.edu) and _Robert G. Wilson v_, Aug 31 2008
|
