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A090570
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Numbers that are congruent to {0, 1} mod 9.
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9
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0, 1, 9, 10, 18, 19, 27, 28, 36, 37, 45, 46, 54, 55, 63, 64, 72, 73, 81, 82, 90, 91, 99, 100, 108, 109, 117, 118, 126, 127, 135, 136, 144, 145, 153, 154, 162, 163, 171, 172, 180, 181, 189, 190, 198, 199, 207, 208, 216, 217, 225, 226
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listen;
history;
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OFFSET
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1,3
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LINKS
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FORMULA
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a(n) = 9*n/2 - 25/4 - 7*(-1)^n/4.
G.f.: x^2*(1+8*x)/( (1+x)*(1-x)^2 ). (End)
E.g.f.: 8 + ((18*x - 25)*exp(x) - 7*exp(-x))/4. - David Lovler, Sep 03 2022
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EXAMPLE
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13 is 1101 in base 2, so a(13+1) = a(14) = 36*1 + 18*1 + 9*0 + 1*1 = 36+18+1 = 55. - Philippe Deléham, Oct 17 2011
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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