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A135650 Even perfect numbers written in base 2. 10
110, 11100, 111110000, 1111111000000, 1111111111111000000000000, 111111111111111110000000000000000, 1111111111111111111000000000000000000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The number of digits of a(n) is equal to 2*A000043(n)-1. The central digit is "1". The first digits are "1". The last digits are "0". The number of digits "1" is equal A000043(n). The number of digits "0" is equal A000043(n)-1.

The concatenation of digits "1" of a(n) gives the n-th Mersenne prime written in binary (see A117293(n)).

Also, the number of digits of a(n) is equal to A133033(n), the number of proper divisors of n-th even perfect number.

LINKS

Table of n, a(n) for n=1..7.

Omar E. Pol, Determinacion geometrica de los numeros primos y perfectos.

EXAMPLE

a(3) = 111110000 because the 3rd even perfect number is 496 and 496 written in base 2 is 111110000. Note that 11111 is the 3rd Mersenne prime A000668(3) = 31 written in base 2.

CROSSREFS

Cf. A000043, A000396, A000668, A090748, A117293.

Cf. A061645, A133033.

Sequence in context: A090490 A267688 A211979 * A193240 A267775 A267867

Adjacent sequences:  A135647 A135648 A135649 * A135651 A135652 A135653

KEYWORD

base,nonn

AUTHOR

Omar E. Pol, Feb 21 2008, Feb 22 2008, Apr 28 2009

STATUS

approved

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Last modified October 19 22:28 EDT 2018. Contains 316378 sequences. (Running on oeis4.)