A225429 Number of n-digit numbers x such that the digits of x^2 occur with frequency 2.

0, 1, 8, 38, 165, 1020, 5360, 24553, 98442

Offset

1,3

Comments

After a(10), all terms are 0.

Links

Table of n, a(n) for n=1..9.

Example

The only two-digit number is 88, whose square is 7744.

Mathematica

cnt = 0; t2 = Table[x = Floor[Sqrt[10] * 10^(n-1)]; While[x < 10^n, If[Union[Last[Transpose[Tally[IntegerDigits[x^2]]]]] == {2}, cnt++]; x++]; cnt, {n, 6}]; Join[{0}, Differences[t2]]

Crossrefs

Cf. A225428.

Sequence in context: A230905 A026640 A122682 * A123518 A197338 A214931

Adjacent sequences: A225426 A225427 A225428 * A225430 A225431 A225432

Keyword

nonn,base

Author

T. D. Noe, Jun 21 2013

Status

approved