login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A329663 Numbers k such that the binary reversal of k (A030101) is equal to the sum of the proper divisors of k (A001065). 0
2, 1881, 49905, 54585, 63405, 196785, 853785, 2094897, 3925449, 32480685, 1925817945, 1994453385, 961201916805 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
a(13) > 1.45*10^11.
a(14) > 5*10^12, if it exists. - Giovanni Resta, Feb 29 2020
LINKS
EXAMPLE
2 is a term since its binary representation is 10, its binary reversal is 01 = 1 which is equal to the sum of the proper divisors of 2.
1881 is a term since its binary representation is 11101011001, its binary reversal is 10011010111 which is equal to 1239, which is also the sum of the proper divisors of 1881: 1 + 3 + 9 + 11 + 19 + 33 + 57 + 99 + 171 + 209 + 627 = 1239.
MATHEMATICA
Select[Range[10^5], DivisorSigma[1, #] - # == IntegerReverse[#, 2] &]
PROG
(PARI) isok(k) = sigma(k) - k == fromdigits(Vecrev(binary(k)), 2); \\ Michel Marcus, Feb 29 2020
CROSSREFS
Sequence in context: A167840 A113917 A259487 * A069793 A230082 A217372
KEYWORD
nonn,base,more
AUTHOR
Amiram Eldar, Feb 28 2020
EXTENSIONS
a(13) from Giovanni Resta, Feb 29 2020
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 2 02:30 EST 2024. Contains 370447 sequences. (Running on oeis4.)