A328333 Expansion of (1 + 4*x - 6*x^2) / ((1 - x) * (1 - 10*x^2)).

1, 5, 9, 49, 89, 489, 889, 4889, 8889, 48889, 88889, 488889, 888889, 4888889, 8888889, 48888889, 88888889, 488888889, 888888889, 4888888889, 8888888889, 48888888889, 88888888889, 488888888889, 888888888889, 4888888888889, 8888888888889, 48888888888889, 88888888888889

Offset: 0

Author

Ilya Gutkovskiy, Oct 12 2019

Keywords

• nonn
• base
• easy

Comments

Number of even palindromes < 10^n.

Links

• Eric Weisstein's World of Mathematics, Palindromic Number
• Index entries for linear recurrences with constant coefficients, signature (1,10,-10).

Crossrefs

Cf. A002113, A029951, A050250, A070199, A328332.

Programs

Mathematica

nmax = 28; CoefficientList[Series[(1 + 4 x - 6 x^2)/((1 - x) (1 - 10 x^2)), {x, 0, nmax}], x]
LinearRecurrence[{1, 10, -10}, {1, 5, 9}, 29]

PARI

Vec((1 + 4*x - 6*x^2) / ((1 - x) * (1 - 10*x^2)) + O(x^30)) \\ Michel Marcus, Oct 13 2019