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A081219 One sixtieth the product of primitive Pythagorean triangles' sides whose odd values differ by 2. 0
1, 34, 259, 1092, 3333, 8294, 17927, 34952, 62985, 106666, 171787, 265420, 396045, 573678, 809999, 1118480, 1514513, 2015538, 2641171, 3413332, 4356373, 5497206, 6865431, 8493464, 10416665, 12673466, 15305499, 18357724, 21878557, 25919998 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

If Y and Z are 2-blocks of a (2n+1)-set X then a(n-2) is the number of 7-subsets of X intersecting both Y and Z. - Milan Janjic, Oct 28 2007

LINKS

Table of n, a(n) for n=1..30.

Milan Janjic, Two Enumerative Functions

Index entries for linear recurrences with constant coefficients, signature (6,-15,20,-15,6,-1).

FORMULA

a(n) = n*(16*n^4 - 1)/15.

G.f.: x*(x^4+28*x^3+70*x^2+28*x+1) / (x-1)^6. - Colin Barker, Oct 06 2014

PROG

(PARI) Vec(x*(x^4+28*x^3+70*x^2+28*x+1)/(x-1)^6 + O(x^100)) \\ Colin Barker, Oct 06 2014

CROSSREFS

Cf. A081752.

Sequence in context: A190422 A209951 A209944 * A254700 A241698 A159776

Adjacent sequences:  A081216 A081217 A081218 * A081220 A081221 A081222

KEYWORD

easy,nonn

AUTHOR

Lekraj Beedassy, Apr 18 2003

EXTENSIONS

More terms from Ray Chandler, Oct 28 2003

STATUS

approved

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Last modified February 22 18:03 EST 2020. Contains 332148 sequences. (Running on oeis4.)