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A294344
a(n) = ((-9*n + 82)*10^n - 1)/81.
2
1, 9, 79, 679, 5679, 45679, 345679, 2345679, 12345679, 12345679, -987654321, -20987654321, -320987654321, -4320987654321, -54320987654321, -654320987654321, -7654320987654321, -87654320987654321, -987654320987654321, -10987654320987654321, -120987654320987654321
OFFSET
0,2
FORMULA
From Colin Barker, Oct 29 2017: (Start)
G.f.: (1 - 12*x + 10*x^2) / ((1 - x)*(1 - 10*x)^2).
a(n) = 21*a(n-1) - 120*a(n-2) + 100*a(n-3) for n>2.
(End)
EXAMPLE
Curious multiplications:
9 * 8 = 72;
79 * 8 = 632;
679 * 8 = 5432;
5679 * 8 = 45432;
45679 * 8 = 365432;
345679 * 8 = 2765432;
2345679 * 8 = 18765432.
9 * 9 = 81;
79 * 9 = 711;
679 * 9 = 6111;
5679 * 9 = 51111;
45679 * 9 = 411111;
345679 * 9 = 3111111;
2345679 * 9 = 21111111.
MATHEMATICA
LinearRecurrence[{21, -120, 100}, {1, 9, 79}, 30] (* Harvey P. Dale, Mar 12 2018 *)
PROG
(PARI) Vec((1 - 12*x + 10*x^2) / ((1 - x)*(1 - 10*x)^2) + O(x^30)) \\ Colin Barker, Oct 29 2017
CROSSREFS
Cf. A294328.
Sequence in context: A293721 A198857 A126632 * A125909 A125421 A163445
KEYWORD
sign,easy
AUTHOR
Seiichi Manyama, Oct 28 2017
STATUS
approved