Smallest square that begins with n

1..49 -> map {|n|
    [n, n.isqrt..Inf -> first {|j| Str(j**2).starts_with(n) }]
}.slices(5).each {|a|
    say a.map { '%2d: %5d %-8s' % (_[0], _[1]**2, "(#{_[1]}^2)") }.join(' ')
}

Output:

 1:     1 (1^2)     2:    25 (5^2)     3:    36 (6^2)     4:     4 (2^2)     5:   529 (23^2)  
 6:    64 (8^2)     7:   729 (27^2)    8:    81 (9^2)     9:     9 (3^2)    10:   100 (10^2)  
11:  1156 (34^2)   12:   121 (11^2)   13:  1369 (37^2)   14:   144 (12^2)   15:  1521 (39^2)  
16:    16 (4^2)    17:  1764 (42^2)   18:  1849 (43^2)   19:   196 (14^2)   20:  2025 (45^2)  
21:  2116 (46^2)   22:   225 (15^2)   23:  2304 (48^2)   24:  2401 (49^2)   25:    25 (5^2)   
26:  2601 (51^2)   27:  2704 (52^2)   28:   289 (17^2)   29:  2916 (54^2)   30:  3025 (55^2)  
31:  3136 (56^2)   32:   324 (18^2)   33:  3364 (58^2)   34:  3481 (59^2)   35: 35344 (188^2) 
36:    36 (6^2)    37:  3721 (61^2)   38:  3844 (62^2)   39:  3969 (63^2)   40:   400 (20^2)  
41: 41209 (203^2)  42:  4225 (65^2)   43:  4356 (66^2)   44:   441 (21^2)   45: 45369 (213^2) 
46:  4624 (68^2)   47:  4761 (69^2)   48:   484 (22^2)   49:    49 (7^2)