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A003555
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Sum{1,2,...,(10^n - 1)/9}, or (10^n -1)/9)((10^n -1)/9 +1)/2 (n-th term is the middle 2(n-1) digits of the (n+9)-th term for n > 1).
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3
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1, 66, 6216, 617716, 61732716, 6172882716, 617284382716, 61728399382716, 6172839549382716, 617283951049382716, 61728395066049382716, 6172839506216049382716, 617283950617716049382716
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Patterned, or almost palindromic, numbers obtained by modification of "half-repdigit" numbers. a[n]=A*(((100^n-1)/9)+B*(10^n - 1)/9)/18, where A=1, B=8-A=7. For example, n = 20: a[20] = 1111111111111111111188888888888888888888/18 = 61728395061728395066049382716049382716, an "almost-palindromic-number". - Labos E. (labos(AT)ana.sote.hu), Oct 28 2004
n is "almost palindromic" if digitlist-Rev[digitlist], besides zeros, contains +1 or -1 in "regular" positions. - Labos E. (labos(AT)ana.sote.hu), Oct 28 2004
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LINKS
| Index to sequences with linear recurrences with constant coefficients, signature (111,-1110,1000)
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FORMULA
| a(n) = A002275(n) * A093142(n).
G.f. x*(-1+45*x) / ( (x-1)*(100*x-1)*(10*x-1) ). - R. J. Mathar, Mar 10 2011
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MATHEMATICA
| f[x_] := 1*((100^x-1)/9) + 7*(10^x-1)/9 Table[f[w], {w, 1, 20}]/18 - Labos E. (labos(AT)ana.sote.hu), Oct 28 2004
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CROSSREFS
| Cf. A098210, A099638.
Sequence in context: A004998 A097316 A099639 * A093266 A197439 A127706
Adjacent sequences: A003552 A003553 A003554 * A003556 A003557 A003558
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KEYWORD
| nonn,base
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AUTHOR
| Daniel Lawson (dlawson(AT)cats.ucsc.edu)
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EXTENSIONS
| Edited by N. J. A. Sloane (njas(AT)research.att.com) at the suggestion of Andrew Plewe, May 31 2007
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