OFFSET
1,2
REFERENCES
David Wells, Curious and Interesting Numbers (Revised), Penguin Books, page 118.
LINKS
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.
Carol Nelson, David E. Penney, Carl Pomerance, 714 and 715, J. Recreational Mathematics 7(2), Spring 1974, 87-89 [copy from Wayback machine]
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. [Warning: As of March 2018 this site appears to have been hacked. Proceed with great caution. The original content should be retrieved from the Wayback machine and added here. - N. J. A. Sloane, Mar 29 2018]
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
KEYWORD
nonn
AUTHOR
STATUS
approved