OFFSET
0,1
COMMENTS
Note that 1 is the only number that has infinitely many cototient-inverses, namely, all the primes.
LINKS
Donovan Johnson, Table of n, a(n) for n = 0..1000
FORMULA
a(n) = min {x: |InvCot(x)| = n}.
a(n) = min { k | A063740(k) = n }. - M. F. Hasler, Jan 11 2018
EXAMPLE
For n = 1, 2, 3, 4, 5, ..., the corresponding inverse sets are as follows: {}, {4}, {6, 8}, {12, 14, 16}, {95, 119, 143, 529}, {75, 155, 203, 299, 323}, ..., {455, 815, 1727, 2567, 2831, 4031, 4247, 4847, 5207, 6431, 6527, 6767, 6887, 7031, 27889}, including 0, 1, 2, 3, 4, 5, ..., 15 numbers.
MATHEMATICA
With[{s = Array[Count[Range[#^2], k_ /; k - EulerPhi@ k == #] &, 300, 2]}, ReplacePart[TakeWhile[First@ FirstPosition[s, #] + 1 & /@ Range[0, Max@ s], IntegerQ], 2 -> 0]] (* Michael De Vlieger, Jan 11 2018 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Aug 13 2001
EXTENSIONS
More terms from David Wasserman, Jul 11 2002
STATUS
approved