OFFSET
1,2
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..1000
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.
FORMULA
Sigma(1, a(n)) = x^8, where the initial values of x are 1, 2, 4, 6 (occurs 85 times), ...
EXAMPLE
Divisors(217)={1,7,31,217}, sum=256=2^8.
Divisors(57337)={1,7,8191,57337}, sum=65536=4^8.
Divisors(1676377)={1,647,2591,1676377}, sum=1679616=6^8.
MATHEMATICA
Select[Range[10^6], IntegerQ@ Surd[DivisorSigma[1, #], 8] &] (* Michael De Vlieger, Aug 01 2017, after _Harvey P.Dale_ at A048257 *)
PROG
(PARI) isok(n) = ispower(sigma(n), 8); \\ Michel Marcus, Dec 30 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
editing