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

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A036428 Square octagonal numbers. 6
1, 225, 43681, 8473921, 1643897025, 318907548961, 61866420601441, 12001766689130625, 2328280871270739841, 451674487259834398561, 87622522247536602581025, 16998317641534841066320321, 3297585999935511630263561281, 639714685669847721430064568225 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Also, numbers simultaneously octagonal and centered octagonal. - Steven Schlicker, Apr 24 2007
LINKS
C. Gill, solution to question no. 8, Mathematical Miscellany, 1 (1836), pp. 220-225, at p. 223.
S. C. Schlicker, Numbers Simultaneously Polygonal and Centered Polygonal, Mathematics Magazine, Vol. 84, No. 5, December 2011, pp. 339-350.
Eric Weisstein's World of Mathematics, Octagonal Square Number.
FORMULA
Let x(n) + y(n)*sqrt(48) = (8+sqrt(48))*(7+sqrt(48))^n, s(n) = (y(n)+1)/2; then a(n) = (1/2)*(2+8*(s(n)^2-s(n))). - Steven Schlicker, Apr 24 2007
a(n+2) = 194*a(n+1) - a(n) + 32 and also a(n+1) = 97*a(n) + 56*sqrt(3*a(n)^2 + a(n)). - Richard Choulet, Sep 26 2007
G.f.: x*(x^2+30x+1)/((1-x)*(1-194x+x^2)).
From Ant King, Nov 15 2011: (Start)
lim_{n->oo} a(n)/a(n-1) = (2 + sqrt(3))^4 = 97 + 56*sqrt(3).
a(n) = (1/12) * ((2 + sqrt(3))^(4n-2) + (2 - sqrt(3))^(4n-2) - 2).
a(n) = floor((1/12) * (2 + sqrt(3))^(4n-2)).
a(n) = (1/12) * ((tan(5*Pi/12))^(4n-2) + (tan(Pi/12))^(4n-2) - 2).
a(n) = floor((1/12) * tan(5*Pi/12)^(4n-2)).
(End)
a(n) = A028230(n)^2. - Bernard Schott, Dec 23 2022
MAPLE
A036428 := proc(n)
option remember;
if n < 4 then
op(n, [1, 225, 43681]) ;
else
195*(procname(n-1)-procname(n-2))+procname(n-3) ;
end if;
end proc: # R. J. Mathar, Nov 11 2011
MATHEMATICA
LinearRecurrence[{195, -195, 1}, {1, 225, 43681}, 12] (* Ant King, Nov 15 2011 *)
PROG
(PARI) Vec(-x*(x^2+30*x+1)/((x-1)*(x^2-194*x+1)) + O(x^20)) \\ Colin Barker, Jun 24 2015
(PARI) vector(15, n, floor((2+sqrt(3))^(4*n-2)/12)) \\ Altug Alkan, Oct 19 2015
(Magma) [Floor(1/12*(2+Sqrt(3))^(4*n-2)): n in [1..20]]; // Vincenzo Librandi, Dec 04 2015
CROSSREFS
Sequence in context: A264194 A339693 A061051 * A183822 A260864 A265420
KEYWORD
nonn,easy
AUTHOR
Jean-Francois Chariot (jean-francois.chariot(AT)afoc.alcatel.fr)
EXTENSIONS
More terms from Eric W. Weisstein
Edited by N. J. A. Sloane, Oct 02 2007
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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 27 21:03 EST 2024. Contains 370378 sequences. (Running on oeis4.)