A107423 - OEIS

%I #5 Mar 30 2012 18:40:01

%S 15,35,143,899,1763,5183,19043,79523,213443,359999,412163,685583,

%T 777923,1192463,1695203,2585663,4536899,5143823,5673923,7225343,

%U 12446783,12659363,12830723,17040383,17892899,18818243,20684303,25100099

%N Numbers k equal prime(n)*prime(n+1) such that k+1 is a square and k-1 is even semiprime.

%e a(1)=15 because 3*5=15: 15+1=4^2 and 15-1=2*7;

%e a(2)=35 because 5*7=35: 35+1=6^2 and 35-1=2*17;

%e a(3)=143 because 11*13=143: 143+1=12^2 and 143-1=2*71;

%e a(4)=899 because 29*31=899: 899+1=30^2 and 899-1=2*449;

%K nonn

%O 1,1

%A _Giovanni Teofilatto_, May 26 2005

%E Terms beyond a(6) from _R. J. Mathar_, Jun 28 2010