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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A020477 Sum of divisors of n is a cube. 19
1, 7, 102, 110, 142, 159, 187, 381, 690, 714, 770, 994, 1034, 1054, 1065, 1113, 1164, 1173, 1265, 1293, 1309, 1633, 1643, 2667, 3638, 3937, 4505, 4830, 4855, 5373, 5671, 5730, 5997, 6486, 6517, 6906, 7130, 7238, 7378, 7455, 7755, 7905, 8148, 8211, 8426 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

David Wells, Curious and Interesting Numbers (Revised), Penguin Books, page 118.

LINKS

T. D. Noe and K. D. Bajpai, Table of n, a(n) for n = 1..10800 (first 1000 terms from T. D. Noe)

Frits Beukers, Florian Luca and Frans Oort, Power Values of Divisor Sums, The American Mathematical Monthly, Vol. 119, No. 5 (May 2012), pp. 373-380.

C. Nelson, D. E. Penney, and C. Pomerance (1974) 714 and 715, J. Recreational Mathematics 7(2), 87-89 (see top of page 89); alternative copy.

EXAMPLE

Factor 381; divisors are 1, 3, 127, 381. Sum is 512. Integral cube root of n is 8. So 381 is in sequence.

MATHEMATICA

Do[If[IntegerQ[DivisorSigma[1, n]^(1/3)], Print[n]], {n, 1, 10^4}]

Select[Range[10000], IntegerQ[Surd[DivisorSigma[1, #], 3]]&] (* Harvey P. Dale, Nov 16 2014 *)

PROG

(PARI) isok(n) = ispower(sigma(n), 3); \\ Michel Marcus, Jul 03 2014

CROSSREFS

Cf. A006532.

Sequence in context: A175345 A142358 A210684 * A203356 A223239 A140633

Adjacent sequences:  A020474 A020475 A020476 * A020478 A020479 A020480

KEYWORD

nonn

AUTHOR

David W. Wilson

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified February 23 21:13 EST 2018. Contains 299587 sequences. (Running on oeis4.)