|
| |
|
|
A306695
|
|
a(n) = gcd(n, psi(n)).
|
|
4
|
|
|
|
1, 1, 1, 2, 1, 6, 1, 4, 3, 2, 1, 12, 1, 2, 3, 8, 1, 18, 1, 4, 1, 2, 1, 24, 5, 2, 9, 4, 1, 6, 1, 16, 3, 2, 1, 36, 1, 2, 1, 8, 1, 6, 1, 4, 9, 2, 1, 48, 7, 10, 3, 4, 1, 54, 1, 8, 1, 2, 1, 12, 1, 2, 3, 32, 1, 6, 1, 4, 3, 2, 1, 72, 1, 2, 15, 4, 1, 6, 1, 16, 27, 2, 1, 12, 1, 2, 3, 8, 1, 18, 7, 4, 1, 2, 5, 96, 1, 14, 9, 20
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,4
|
|
|
COMMENTS
|
Here psi(n) is Dedekind's psi function A001615.
a(n) <= n <= A001615(n).
a(n) = n iff a(n) * 2 = A001615(n), n > 1.
a(n) = 1 iff either n=2 or n is in A255602. - Robert Israel, Mar 12 2019
|
|
|
LINKS
|
Robert Israel, Table of n, a(n) for n = 1..10000
Wikipedia, Dedekind psi function
|
|
|
FORMULA
|
a(n) = gcd(n, A001615(n)).
|
|
|
MAPLE
|
f:= proc(n) local p; igcd(n, n*mul(1+1/p, p=numtheory:-factorset(n))) end proc:
map(f, [$1..100]); # Robert Israel, Mar 11 2019
|
|
|
MATHEMATICA
|
psi[n_] := If[n == 1, 1, n Times @@ (1 + 1/FactorInteger[n][[All, 1]])];
a[n_] := GCD[n, psi[n]];
Array[a, 100] (* Jean-François Alcover, Jun 08 2020 *)
|
|
|
PROG
|
(PARI) dpsi(n) = n * sumdivmult(n, d, issquarefree(d)/d); \\ A001615
a(n) = gcd(n, dpsi(n)); \\ Michel Marcus, Mar 05 2019
|
|
|
CROSSREFS
|
Cf. A001615, A255602.
Sequence in context: A154744 A285038 A243145 * A242926 A189733 A306927
Adjacent sequences: A306692 A306693 A306694 * A306696 A306697 A306698
|
|
|
KEYWORD
|
nonn
|
|
|
AUTHOR
|
Torlach Rush, Mar 05 2019
|
|
|
STATUS
|
approved
|
| |
|
|
