This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A088981 #18 Jan 05 2025 13:36:06
%S A088981 7,11,17,25,37,55,83,127,197,309,489,779,1247,2003,3225,5201,8397,
%T A088981 13567,21931,35463,57357,92781,150097,242835,392887,635675,1028513,
%U A088981 1664137,2692597,4356679,7049219,11405839,18454997
%N A088981 a(n+2) = a(n+1) + a(n) - (2*n + 1) where a(0)=7, a(1)=11.
%D A088981 J. Baylis and R. Haggarty, Alice in Numberland, A Student's Guide to the Enjoyment of Higher Mathematics, Macmillan Education 1988.
%D A088981 G. Buckwell, Mastering Mathematics, Palgrave Master Series, 2nd Ed. 1997.
%D A088981 R. P. C. Forman, Additional Mathematics Pure & Applied, Stanley Thornes, 1989.
%H A088981 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (3,-2,-1,1).
%F A088981 a(n) = (2*alpha^(n+3) - 2*beta^(n+3) + 2*sqrt(5)*n + 3*sqrt(5)) / sqrt(5) where alpha = (1 + sqrt(5)) / 2 and beta = (1 - sqrt(5)) / 2.
%t A088981 LinearRecurrence[{3,-2,-1,1},{7,11,17,25},40] (* _Harvey P. Dale_, Jun 08 2018 *)
%o A088981 (PARI) a=[7,11];for(n=2,10,a=concat(a,a[#a]+a[#a-1]-2*n+3)); a
%K A088981 easy,nonn
%O A088981 0,1
%A A088981 _Kurmang. Aziz. Rashid_, Dec 01 2003