A133328 Values of n such that the sum of the 7-gonal number (5*n^2 - 3*n)/2 and the following 7-gonal number is a 7-gonal number.

0, 170, 13622, 6672192, 534017484, 261563278454, 20934553401986, 10253803635289356, 820676361930645528, 401969609849050063298, 32172154719470612594510, 15758012635048656946126680, 1261212808492010592999343332, 617745610917207839753008053902

Offset

1,2

Comments

Both bisections of the sequence satisfy the recurrence relation a(n+2) = 39202*a(n+1) - a(n) + 7840.

Also nonnegative integers x in the solution to 10*x^2-5*y^2+4*x+3*y+2 = 0, the corresponding values of y being A133327. - Colin Barker, Dec 05 2014

Links

Colin Barker, Table of n, a(n) for n = 1..436

Index entries for linear recurrences with constant coefficients, signature (1,39202,-39202,-1,1).

Formula

G.f.: 2*x^2*(6*x^3+2885*x^2-6726*x-85) / ((x-1)*(x^2-198*x+1)*(x^2+198*x+1)). - Colin Barker, Dec 05 2014

Prog

(PARI) concat(0, Vec(2*x^2*(6*x^3+2885*x^2-6726*x-85)/((x-1)*(x^2-198*x+1)*(x^2+198*x+1)) + O(x^100))) \\ Colin Barker, Dec 05 2014

Crossrefs

Cf. A133324, A133327.

Sequence in context: A187520 A210784 A178499 * A098244 A250957 A114048

Adjacent sequences: A133325 A133326 A133327 * A133329 A133330 A133331

Keyword

nonn,easy

Author

Richard Choulet, Oct 18 2007

Extensions

More terms from Colin Barker, Dec 05 2014

Status

approved