OFFSET
1,2
COMMENTS
n - tau(n) = A049820(n) is the number of positive integers < n that do not divide n.
LINKS
Robert Israel, Table of n, a(n) for n = 1..1000
EXAMPLE
4 - tau(4) = 4 - 3 = 1^2 so 4 is in the sequence.
MAPLE
filter:= proc(n) local t;
t:= numtheory:-tau(n);
issqr(n-t)
end proc;
select(filter, [$1..10^4]);
MATHEMATICA
Select[Range[10^4], IntegerQ[Sqrt[# - DivisorSigma[0, #]]]&] (* Jean-François Alcover, Apr 12 2019 *)
PROG
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert Israel, Jul 20 2014
STATUS
approved