This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A253411 Indices of centered octagonal numbers (A016754) which are also centered pentagonal numbers (A005891). 3
 1, 76, 646, 108871, 930811, 156991186, 1342228096, 226381180621, 1935491982901, 326441505463576, 2790978097114426, 470728424497295251, 4024588480547018671, 678790061683594287646, 5803453797970703808436, 978814798219318465489561, 8368576352085274344745321 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also positive integers y in the solutions to 5*x^2 - 8*y^2 - 5*x + 8*y = 0, the corresponding values of x being A253410. LINKS Colin Barker, Table of n, a(n) for n = 1..633 Index entries for linear recurrences with constant coefficients, signature (1,1442,-1442,-1,1). FORMULA a(n) = a(n-1) + 1442*a(n-2) - 1442*a(n-3) - a(n-4) + a(n-5). G.f.: -x*(x^4 + 75*x^3 - 872*x^2 + 75*x + 1) / ((x-1)*(x^2 - 38*x + 1)*(x^2 + 38*x + 1)). EXAMPLE 76 is in the sequence because the 76th centered octagonal number is 22801, which is also the 96th centered pentagonal number. MATHEMATICA LinearRecurrence[{1, 1442, -1442, -1, 1}, {1, 76, 646, 108871, 930811}, 20] (* Harvey P. Dale, Feb 04 2016 *) PROG (PARI) Vec(-x*(x^4+75*x^3-872*x^2+75*x+1)/((x-1)*(x^2-38*x+1)*(x^2+38*x+1)) + O(x^100)) CROSSREFS Cf. A005891, A016754, A253410, A253579. Sequence in context: A129626 A200167 A178262 * A185481 A007250 A137061 Adjacent sequences:  A253408 A253409 A253410 * A253412 A253413 A253414 KEYWORD nonn,easy AUTHOR Colin Barker, Dec 31 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 | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 12 15:11 EST 2019. Contains 329960 sequences. (Running on oeis4.)