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!)
A275411 Least k such that sigma(k*n) = sigma(k*n-1), or 0 if no such k exists. 0
15, 479, 5, 155257, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
See also A275337.
From Michael De Vlieger, Jul 27 2016: (Start)
Terms 6 through 60, with 0 signifying no such k <= 10^6: {0, 195, 99107, 23, 372601, 7257, 0, 105, 1439, 1, 312646, 158, 0, 31894, 0, 65, 4213, 9, 0, 119, 10559, 717, 59677, 5607, 0, 2086, 156323, 2419, 79, 39, 0, 16378, 15947, 35, 0, 362, 0, 12154, 544409, 97, 17236, 9362, 0, 15093, 0, 717, 261103, 4347, 0, 2681, 0, 38051, 3343, 1353, 0}.
n such that a(n) = 0 in above data: {6, 12, 18, 20, 24, 30, 36, 40, 42, 48, 50, 54, 56, 60}, i.e., multiples of 2 and 3, and 2 and 5. (End)
LINKS
EXAMPLE
a(2) = 479 because sigma(479*2) = sigma(479*2-1).
MATHEMATICA
Table[k = 1; While[DivisorSigma[1, k n] != DivisorSigma[1, k n - 1], k++]; k, {n, 5}] (* Michael De Vlieger, Jul 27 2016 *)
PROG
(PARI) a(n) = {my(k = 2); while (sigma(k*n) != sigma(k*n-1), k++); k; } \\ Michel Marcus, Jul 27 2016
CROSSREFS
Sequence in context: A279922 A375727 A129892 * A289185 A079610 A218803
KEYWORD
nonn,more
AUTHOR
Altug Alkan, Jul 27 2016
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 August 30 15:38 EDT 2024. Contains 375545 sequences. (Running on oeis4.)