A258441 9-gonal numbers (A001106) that are the sum of two consecutive 9-gonal numbers.

24486, 959892121, 37629690894906, 1475159141502204841, 57829188627539743273926, 2267019851101653874322234161, 88871712145057846553640480297546, 3483948857243537849494160234302156081, 136577763012789458630812222951472642381766

Offset: 1

Author

Colin Barker, May 30 2015

Keywords

• nonn
• easy

Examples

			24486 is in the sequence because A001106(84) = 24486 = 12036 + 12450 = A001106(59) + A001106(60), where A001106(k) is the k-th 9-gonal number.
		

Links

• Colin Barker, Table of n, a(n) for n = 1..217
• Index entries for linear recurrences with constant coefficients, signature (39203,-39203,1).

Crossrefs

Cf. A001106, A258442, A258443, A258444.

Programs

PARI

Vec(-x*(x^2-32537*x+24486)/((x-1)*(x^2-39202*x+1)) + O(x^20))

Formula

a(n) = 39203*a(n-1) - 39203*a(n-2) + a(n-3).

G.f.: -x*(x^2-32537*x+24486) / ((x-1)*(x^2-39202*x+1)).

a(n) = (46+(89-36*sqrt(2))*(19601+13860*sqrt(2))^(-n)+(89+36*sqrt(2))*(19601+13860*sqrt(2))^n)/224. - Colin Barker, Mar 07 2016