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A145720
Numbers x such that there exists n in N with (x+1)^3-x^3=127*n^2.
3
6, 13201, 26799038, 54402034953, 110436104156566, 224185237035795041, 455095920746559777678, 923844494930279312892313, 1875403869612546258611618726, 3807068931468973974702273122481, 7728348055478147556099355827018718, 15688542745551708069907717626574876073
OFFSET
1,1
FORMULA
a(n+2) = 2030*a(n+1)-a(n)+1014.
a(n) = A145718(n)/127. - Colin Barker, Oct 18 2014
G.f.: x*(7*x^2-1015*x-6) / ((x-1)*(x^2-2030*x+1)). - Colin Barker, Oct 18 2014
EXAMPLE
a(1)=6 because the first relation is 7^3-6^3=127*1^2.
MATHEMATICA
CoefficientList[Series[(7 x^2 - 1015 x - 6)/((x - 1) (x^2 - 2030 x + 1)), {x, 0, 20}], x] (* Vincenzo Librandi, Oct 18 2014 *)
PROG
(PARI) Vec(x*(7*x^2-1015*x-6)/((x-1)*(x^2-2030*x+1)) + O(x^20)) \\ Colin Barker, Oct 18 2014
(Magma) I:=[6, 13201]; [n le 2 select I[n] else 2030*Self(n-1)-Self(n-2)+1014: n in [1..20]]; // Vincenzo Librandi, Oct 18 2014
CROSSREFS
Cf. A145718.
Sequence in context: A146202 A227889 A242676 * A093897 A062782 A036773
KEYWORD
easy,nonn
AUTHOR
Richard Choulet, Oct 16 2008
EXTENSIONS
Editing and more terms from Colin Barker, Oct 18 2014
STATUS
approved