1,2
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.
Cf. A008850.
Sequence in context: A033502 A050794 A138130 * A130876 A008745 A179914
Adjacent sequences: A048946 A048947 A048948 * A048950 A048951 A048952
nonn
Eric Weisstein (eric(AT)weisstein.com)