Sums of Factorials

For every positive integer n, let us denote `n! = 1*2*3*...*n`

Find all integers n such that the sum `1! + 2! + 3! + ... + n!` is the square of an integer.

(Solution format: a,b,c,... i.e., the three smallest numbers separated by commas with no spaces, and three dots after if there are more solutions)

Difficulty level (1 very easy - 10 very hard): 2

Topics:
Number Theory -> Modular Arithmetic / Remainder Arithmetic Algebra -> Sequences
Sources:
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