login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A031876 a(n) = Sum_{k=0..n} floor(k^(1/3)). 9
0, 1, 2, 3, 4, 5, 6, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 48, 51, 54, 57, 60, 63, 66, 69, 72, 75, 78, 81, 84, 87, 90, 93, 96, 99, 102, 105, 108, 111, 114, 117, 120, 123, 126, 129, 132, 135, 138, 141, 144, 147, 150, 153, 156, 160 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

REFERENCES

K. H. Rosen, Discrete Mathematics and Its Application, 6th Edition, McGraw-Hill, 2007, Ex. 26 of section 2.4.

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..1000

FORMULA

a(0) = 0, a(1) = 1, a(n) = 2*a(n-1) - a(n-2) if n not a perfect cube, else a(n) = 2*a(n-1) - a(n-2) + 1 if n is a perfect cube.

a(n) = -1/4*floor(n^(1/3))*(floor(n^(1/3))^3+2*floor(n^(1/3))^2+floor(n^(1/3))-4*(n+1)). - John M. Campbell, Mar 22 2016

G.f.: Sum_{k>=1} x^(k^3)/(1 - x)^2. - Ilya Gutkovskiy, Dec 22 2016

a(n) = (3/4)*n^(4/3) + O(n). - Charles R Greathouse IV, Aug 23 2017

MATHEMATICA

Accumulate[Floor[Surd[Range[0, 70], 3]]] (* Harvey P. Dale, Nov 03 2013 *)

Table[Sum[Floor[i^(1/3)], {i, 0, n}], {n, 0, 50}] (* G. C. Greubel, Dec 22 2016 *)

PROG

(PARI) a(n) = sum(k=1, n, sqrtnint(k, 3)); \\ Michel Marcus, Mar 12 2016

(PARI) a(n)=my(t=sqrtnint(n, 3)); t*(4*n-t^3-2*t^2-t+4)/4 \\ Charles R Greathouse IV, Aug 23 2017

CROSSREFS

Cf. A022554.

Sequence in context: A277417 A246885 A033059 * A292621 A280693 A281613

Adjacent sequences:  A031873 A031874 A031875 * A031877 A031878 A031879

KEYWORD

nonn,easy

AUTHOR

Michel Tixier (tixier(AT)dyadel.net)

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 20 19:57 EDT 2019. Contains 328269 sequences. (Running on oeis4.)