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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
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
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
MATHEMATICA
LinearRecurrence[{6, -15, 20, -15, 6, -1}, {1, 34, 259, 1092, 3333, 8294}, 30] (* Harvey P. Dale, Feb 11 2024 *)
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: A209951 A209944 A371403 * A254700 A241698 A159776
KEYWORD
easy,nonn
AUTHOR
Lekraj Beedassy, Apr 18 2003
EXTENSIONS
More terms from Ray Chandler, Oct 28 2003
STATUS
approved