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Search: id:A138831
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| A138831 |
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n-th perfect number minus 1, written in base 2. |
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+0
2
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| 101, 11011, 111101111, 1111110111111, 1111111111110111111111111, 111111111111111101111111111111111, 1111111111111111110111111111111111111
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Subset of A138148, cyclops numbers with binary digits, only.
Subset of A002113, palindromes in base 10.
a(n) has 2*A090748(n) digits 1.
The number of digits of a(n) is 2*A000043(n)-1, equal to A133033(n), the number of proper divisors of n-th perfect number.
a(n) = (A135627(n) written in base 2).
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LINKS
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O. E. Pol, Determinacion geometrica de los numeros primos y perfectos.
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FORMULA
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a(n) = A138148(A090748(n)).
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EXAMPLE
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n ... A000396(n) - 1 = A135627(n) ............. a(n)
1 ............ 6 - 1 = ...... 5 ............... 101
2 ........... 28 - 1 = ..... 27 .............. 11011
3 .......... 496 - 1 = .... 495 ............ 111101111
4 ......... 8128 - 1 = ... 8127 .......... 1111110111111
5 ..... 33550336 - 1 = 33550335 .... 1111111111110111111111111
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CROSSREFS
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Cf. A000043, A000396, A090748, A133033, A134808, A135627, A138131, A138148.
Sequence in context: A097727 A083981 A138148 this_sequence A068160 A082435 A136098
Adjacent sequences: A138828 A138829 A138830 this_sequence A138832 A138833 A138834
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KEYWORD
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nonn
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AUTHOR
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Omar E. Pol (info(AT)polprimos.com), Apr 08 2008, Apr 09 2008, Apr 14 2008
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