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 A138831 n-th perfect number minus 1, written in base 2. 2
 101, 11011, 111101111, 1111110111111, 1111111111110111111111111, 111111111111111101111111111111111, 1111111111111111110111111111111111111 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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). LINKS FORMULA a(n) = A138148(A090748(n)). EXAMPLE 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 CROSSREFS Cf. A000043, A000396, A090748, A133033, A134808, A135627, A138131, A138148. Sequence in context: A083981 A267779 A138148 * A267920 A300570 A171825 Adjacent sequences:  A138828 A138829 A138830 * A138832 A138833 A138834 KEYWORD nonn,base,less AUTHOR Omar E. Pol, Apr 08 2008, Apr 09 2008, Apr 14 2008 STATUS approved

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Last modified November 26 01:22 EST 2020. Contains 338631 sequences. (Running on oeis4.)