# math

posted by
**Amanda**
.

smallest of two triangular numbers whose sum and difference are also triangular numbers

My guess would be 15.

21 - 15 = 6 and 15 + 21 = 36.

posted by
**Amanda**
.

smallest of two triangular numbers whose sum and difference are also triangular numbers

My guess would be 15.

21 - 15 = 6 and 15 + 21 = 36.