The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A260786 Twice the Euler or up/down numbers A000111. 4
 2, 2, 2, 4, 10, 32, 122, 544, 2770, 15872, 101042, 707584, 5405530, 44736512, 398721962, 3807514624, 38783024290, 419730685952, 4809759350882, 58177770225664, 740742376475050, 9902996106248192, 138697748786275802, 2030847773013704704, 31029068327114173810, 493842960380415967232 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS S. T. Thompson, Problem E754: Skew Ordered Sequences, Amer. Math. Monthly, 54 (1947), 416-417. [Annotated scanned copy] FORMULA a(0)=a(1)=2; thereafter a(n) = (1/4)*Sum_{k=1..n} binomial(n-1, k-1)*a(k-1)*a(n-k). MAPLE f:=proc(n) option remember; if n <= 1 then 2 else (1/4)*add(binomial(n-1, k-1)*f(k-1)*f(n-k), k=1..n); fi; end; [seq(f(n), n=0..30)]; CROSSREFS Cf. A000111. Apart from initial terms, same as A001250. Sequence in context: A307522 A130707 A131562 * A067920 A107902 A142974 Adjacent sequences:  A260783 A260784 A260785 * A260787 A260788 A260789 KEYWORD nonn AUTHOR N. J. A. Sloane, Aug 04 2015 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 26 12:20 EDT 2021. Contains 346294 sequences. (Running on oeis4.)