[seqfan] Middle digit in square numbers

[Lars Blomberg]

Hello,

 

Numbers k such that the middle digit of k^2 is d.

Obviously k^2 must have an odd number of digits.

 

Examples for d=4: 2^2 = 4, 12^2 = 144, 21^2 = 441, 29^2 = 841, 102 = 10404,
...

 

Start of sequences for d =  0..9

0: 10, 20, 30, 100, 105, 138, 145, .

1: 1, 110, 119, 123, 127, 131, 142, .

2: 11, 15, 18, 23, 25, 27, 101, 106,.

3: 111, 124, 128, 139, 146, 156, 177, .

4: 2, 12, 21, 29, 102, 107, 116, 120,.

5: 16, 112, 150, 163, 166, 169, 172,.

6: 13, 19, 31, 103, 108, 117, 121, .

7: 24, 26, 113, 137, 144, 154, 181,.

8: 17, 22, 28, 104, 109, 122, 126, .

9: 3, 14, 114, 118, 130, 134, 148, .

 

It was a surprise to me that none of these sequences are in OEIS.

Maybe they are too simple to be included?

 

/Lars Blomberg