I believe that the next two numbers are 260 & 369.
More of the series might be: 1, 5, 15, 34, 56, 111, 175, 260, 369, 505 . . .
The equation that generates the series is
M = 1/2*2*(n^2 + 1)
This is the series of magic constants, that is, the sums and rows of magic squares where the square starts with a 1. A 3 x 3 magic square containing the numbers 1 through 9 will have rows and columns totaling 15. A 4x4 magic square starting with 1 will total 34; a 5x5 will total 111; and so forth.
I had to put on my thinking cap, then search the web, then put on my thinking cap again to figure this one out! Thanks, CWanamaker!
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