The following pictures show n unit circles covering the largest known circle (of radius r ).

n=1

r = 1

Trivial.
n=3

r = 2 / √3 = 1.154+

Trivial.
n=4

r = √2 = 1.414+

Trivial.
n=5

r = 1.641+

Proved by Károly Bezdek

in 1983.

n=6

r = 1.798+

Proved by Károly Bezdek

in 1979.
n=7

r = 2

Trivial.
n=8

r = 2.246+

Proved by Gábor Fejes Tóth

in 1996.
n=9

r = √2 + 1 = 2.414+

Proved by Gábor Fejes Tóth

in 1996.

n=10

r = 2.532+

Proved by Gábor Fejes Tóth

in 2005.
n=11

r = 2.631+

Found by Hans Melissen

in 1997.
n=12

r = 2.769+

Found by Hans Melissen

in 1997.
n=13

r = 2.884+

Found by Jeremy Tan

in 2018.

n=14

r = 3.014+

Found by Jeremy Tan

in 2018.
n=15

r = 3.143+

Found by Jeremy Tan

in 2018.
n=16

r = 3.244+

Found by Jeremy Tan

in 2018.
n=17

r = 3.349+

Found by Jeremy Tan

in 2018.

n=18

r = 3.446+

Found by Jeremy Tan

in 2018.
n=19

r = √13 = 3.605+

Found by Jeremy Tan

in 2018.
n=20

r = 3.692+

Found by Jeremy Tan

in 2018.
n=21

r = 3.804+

Found by Jeremy Tan

in 2018.

n=22

r = 3.948+

Found by Jeremy Tan

in 2018.
n=23

r = 4.000+

Found by Jeremy Tan

in 2018.
n=24

r = 4.076+

Found by Jeremy Tan

in 2018.
n=25

r = √6 + √3 = 4.181+

Found by Jeremy Tan

in 2018.