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A026396
Sum_{T(i,j)}, 0<=j<=i, 0<=i<=n, where T is the array in A026386.
1
3, 7, 17, 37, 87, 187, 437, 937, 2187, 4687, 10937, 23437, 54687, 117187, 273437, 585937, 1367187, 2929687, 6835937, 14648437, 34179687, 73242187, 170898437, 366210937, 854492187, 1831054687, 4272460937, 9155273437, 21362304687, 45776367187, 106811523437
OFFSET
0,1
FORMULA
G.f.: (3+4*x-5*x^2) / ((1-x)*(1-5*x^2)). - Ralf Stephan, Apr 30 2004
From Colin Barker, Nov 25 2016: (Start)
a(n) = (7*5^(n/2) - 1)/2 for n even.
a(n) = (6*5^((n+1)/2) - 2)/4 for n odd.
a(n) = a(n-1) + 5*a(n-2) - 5*a(n-3) for n>2. (End)
a(n) = (3-(-1)^n-(13+(-1)^n)*5^((1-(-1)^n+2*n)/4))/(2*(-1)^n-6). - Wesley Ivan Hurt, Oct 02 2021
MATHEMATICA
LinearRecurrence[{1, 5, -5}, {3, 7, 17}, 50] (* Paolo Xausa, Sep 16 2024 *)
PROG
(PARI) Vec((-5*x^2 + 4*x + 3)/(5*x^3 - 5*x^2 - x + 1) + O(x^40)) \\ Colin Barker, Nov 25 2016
CROSSREFS
Cf. A026386.
Sequence in context: A178941 A178155 A330457 * A176502 A319003 A141199
KEYWORD
nonn,easy
STATUS
approved