The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A241851 a(n) = n^2 + 21. 3
 21, 22, 25, 30, 37, 46, 57, 70, 85, 102, 121, 142, 165, 190, 217, 246, 277, 310, 345, 382, 421, 462, 505, 550, 597, 646, 697, 750, 805, 862, 921, 982, 1045, 1110, 1177, 1246, 1317, 1390, 1465, 1542, 1621, 1702, 1785, 1870, 1957, 2046, 2137, 2230, 2325 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA G.f.: (21 - 41*x + 22*x^2)/(1 - x)^3. a(n) = a(-n) = 3*a(n-1) - 3*a(n-2) + a(n-3) = a(n-1) + 2*n - 1. From Amiram Eldar, Nov 04 2020: (Start) Sum_{n>=0} 1/a(n) = (1 + sqrt(21)*Pi*coth(sqrt(21)*Pi))/42. Sum_{n>=0} (-1)^n/a(n) = (1 + sqrt(21)*Pi*cosech(sqrt(21)*Pi))/42. (End) MATHEMATICA Table[n^2 + 21, {n, 0, 60}] PROG (Magma) [n^2+21: n in [0..60]]; (PARI) a(n)=n^2+21 \\ Charles R Greathouse IV, Jun 17 2017 CROSSREFS Cf. similar sequence listed in A114962. Sequence in context: A141439 A323419 A333908 * A295747 A125737 A349248 Adjacent sequences: A241848 A241849 A241850 * A241852 A241853 A241854 KEYWORD nonn,easy AUTHOR Vincenzo Librandi, May 01 2014 STATUS approved

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

Last modified February 21 12:33 EST 2024. Contains 370235 sequences. (Running on oeis4.)