OFFSET
1,2
COMMENTS
LINKS
Zak Seidov, Table of n, a(n) for n = 1..10000
O. Ore, On the averages of the divisors of a number, Amer. Math. Monthly, 55 (1948), 615-619.
EXAMPLE
The first four terms are 1,2,3,and 3, being the averages of the divisors of the first four arithmetic numbers, 1,3,5 and 6, respectively. Indeed, 1/1=1, (1+3)/2=2, (1+5)/2=3 and (1+2+3+6)/4=3.
MAPLE
with(numtheory): p:=proc(n) if type(sigma(n)/tau(n), integer)=true then sigma(n)/tau(n) else fi end: seq(p(n), n=1..130);
MATHEMATICA
a003601[n_Integer] :=
Select[Range[n], IntegerQ[DivisorSigma[1, #]/DivisorSigma[0, #]] &]; a102187[n_Integer] :=
Map[DivisorSigma[1, #]/DivisorSigma[0, #] &, a003601[n]]; a102187[200] (* Michael De Vlieger, Aug 05 2014 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Feb 16 2005
STATUS
approved