A107423 Numbers k equal prime(n)*prime(n+1) such that k+1 is a square and k-1 is even semiprime.

15, 35, 143, 899, 1763, 5183, 19043, 79523, 213443, 359999, 412163, 685583, 777923, 1192463, 1695203, 2585663, 4536899, 5143823, 5673923, 7225343, 12446783, 12659363, 12830723, 17040383, 17892899, 18818243, 20684303, 25100099

Offset

1,1

Links

Table of n, a(n) for n=1..28.

Example

a(1)=15 because 3*5=15: 15+1=4^2 and 15-1=2*7;
a(2)=35 because 5*7=35: 35+1=6^2 and 35-1=2*17;
a(3)=143 because 11*13=143: 143+1=12^2 and 143-1=2*71;
a(4)=899 because 29*31=899: 899+1=30^2 and 899-1=2*449;

Crossrefs

Sequence in context: A194580 A210503 A037074 * A027442 A208728 A219689

Adjacent sequences: A107420 A107421 A107422 * A107424 A107425 A107426

Keyword

nonn

Author

Giovanni Teofilatto, May 26 2005

Extensions

Terms beyond a(6) from R. J. Mathar, Jun 28 2010

Status

approved