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!)
 A016838 a(n) = (4n + 3)^2. 11
 9, 49, 121, 225, 361, 529, 729, 961, 1225, 1521, 1849, 2209, 2601, 3025, 3481, 3969, 4489, 5041, 5625, 6241, 6889, 7569, 8281, 9025, 9801, 10609, 11449, 12321, 13225, 14161, 15129, 16129, 17161, 18225 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS If Y is a fixed 2-subset of a (4n+1)-set X then a(n-1) is the number of 3-subsets of X intersecting Y. - Milan Janjic, Oct 21 2007 A bisection of A016754. Sequence arises from reading the line from 9, in the direction 9, 49, ... in the square spiral whose vertices are the squares A000290. - Omar E. Pol, May 24 2008 Using (n,n+1) to generate a Pythagorean triangle with sides of lengths x=0} 1/a(n) = Pi^2/16 - G/2, where G is the Catalan constant (A006752). - Amiram Eldar, Jun 28 2020 Product_{n>=0} (1 - 1/a(n)) = Gamma(3/4)^2/sqrt(Pi) = A068465^2 * A087197. - Amiram Eldar, Feb 01 2021 MAPLE A016838:=n->(4*n + 3)^2; seq(A016838(n), n=0..50); # Wesley Ivan Hurt, Feb 24 2014 MATHEMATICA Table[(4*n + 3)^2, {n, 0, 40}] (* Vaclav Kotesovec, Nov 14 2017 *) PROG (MAGMA) [(4*n+3)^2: n in [0..50]]; // Vincenzo Librandi, Apr 26 2011 (PARI) a(n)=(4*n+3)^2 \\ Charles R Greathouse IV, Jun 17 2017 CROSSREFS Cf. A000290, A001539, A016742, A016754, A016802, A016814, A016826, A068465, A087197. Sequence in context: A012111 A138998 A339125 * A087691 A014730 A212503 Adjacent sequences:  A016835 A016836 A016837 * A016839 A016840 A016841 KEYWORD nonn,easy AUTHOR 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 April 20 06:59 EDT 2021. Contains 343125 sequences. (Running on oeis4.)