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A070252
Number of n-digit palindromes.
11
10, 9, 90, 90, 900, 900, 9000, 9000, 90000, 90000, 900000, 900000, 9000000, 9000000, 90000000, 90000000, 900000000, 900000000, 9000000000, 9000000000, 90000000000, 90000000000, 900000000000, 900000000000, 9000000000000
OFFSET
1,1
FORMULA
From Colin Barker, Aug 19 2013: (Start)
a(n) = 10*a(n-2) for n>3.
G.f.: x*(10*x^2-9*x-10) / (10*x^2-1). (End)
E.g.f.: x + 9*(cosh(sqrt(10)*x) - 1 + sqrt(10)*sinh(sqrt(10)*x))/10. - Stefano Spezia, Jun 11 2022
MATHEMATICA
LinearRecurrence[{0, 10}, {10, 9, 90}, 25] (* Stefano Spezia, Jun 11 2022 *)
CROSSREFS
A variant of A050683, which is the principal entry for this sequence. Cf. A016115.
Partial sums give A070199.
Sequence in context: A241285 A052196 A243035 * A038311 A244960 A282560
KEYWORD
base,nonn,easy
AUTHOR
Amarnath Murthy, May 06 2002
STATUS
approved