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A135577
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Numbers that have only the digit "1" as first, central and final digit. For numbers with 5 or more digits the rest of digits are "0".
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12
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1, 111, 10101, 1001001, 100010001, 10000100001, 1000001000001, 100000010000001, 10000000100000001, 1000000001000000001, 100000000010000000001, 10000000000100000000001
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Also, equal to A135576(n), written in base 2.
Essentially the same as A066138. R. J. Mathar (mathar(AT)strw.leidenuniv.nl) Apr 29 2008
a(n) has 2n-1 digits.
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FORMULA
| a(n)=A135576(n), written in base 2.
Also, a(1)=1, for n>1; a(n)=(concatenation of 1, n-2 digits 0, 1, n-2 digits 0 and 1).
a(n)=10^(2*n-2)+10^(n-1)+1-2*{C[2*(n-1),n-1] mod 2}, with n>=1 [From Paolo P. Lava (paoloplava(AT)gmail.com), Nov 26 2008]
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EXAMPLE
| ----------------------------
n ............ a(n)
----------------------------
1 ............. 1
2 ............ 111
3 ........... 10101
4 .......... 1001001
5 ......... 100010001
6 ........ 10000100001
7 ....... 1000001000001
8 ...... 100000010000001
9 ..... 10000000100000001
10 ... 1000000001000000001
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CROSSREFS
| Cf. A001576, A135576.
Cf. A138118, A138119, A138120, A138147, A138826.
Sequence in context: A008396 A129051 A012039 * A153498 A152764 A138146
Adjacent sequences: A135574 A135575 A135576 * A135578 A135579 A135580
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KEYWORD
| nonn,base
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AUTHOR
| Omar E. Pol (info(AT)polprimos.com), Feb 24 2008
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