#math trivia #81 solution

Burt Kaliski Jr. (@modulomathy)
3/21/12 2:54 PM
#math trivia for #March21: #81 is a square, and the sum of its digits is a square. What other days this year have this property?

The one-digit squares all have this property: 1, 4, 9.

Among the 15 other day-numbers not already mentioned that are squares, the ones whose digits sum to a square are 36, 100, 121, 144, 169, 196, 225, 324.

The long stretch of consecutive squares from 81 to 225 that have the property is quite interesting. Any ideas why they all work out this way?

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