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!)
A368674 Sum of the squarefree numbers less than n that do not divide n. 1
0, 0, 2, 3, 5, 5, 16, 21, 20, 16, 33, 33, 44, 48, 63, 84, 86, 92, 103, 105, 112, 130, 165, 177, 183, 173, 211, 191, 214, 202, 273, 302, 290, 318, 359, 395, 406, 422, 465, 503, 520, 508, 603, 611, 623, 621, 692, 728, 732, 722, 719, 749, 790, 832, 827, 875, 876, 924, 1013, 1001 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
LINKS
FORMULA
a(n) = Sum_{k=1..n} k * mu(k)^2 * (ceiling(n/k) - floor(n/k)).
EXAMPLE
a(12) = 33. There are 4 squarefree numbers less than 12 that do not divide 12, namely: 5, 7, 10, and 11. Their sum is 5 + 7 + 10 + 11 = 33.
MATHEMATICA
Table[Sum[k*MoebiusMu[k]^2 (Ceiling[n/k] - Floor[n/k]), {k, n}], {n, 100}]
PROG
(PARI) a(n) = sum(k=1, n-1, if ((n % k) && issquarefree(k), k)); \\ Michel Marcus, Jan 03 2024
CROSSREFS
Cf. A008683 (mu), A368673.
Sequence in context: A342437 A079022 A368706 * A095296 A256301 A226609
KEYWORD
nonn,easy
AUTHOR
Wesley Ivan Hurt, Jan 02 2024
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 April 12 10:51 EDT 2024. Contains 371632 sequences. (Running on oeis4.)