another approach might be to treat numbers as letters, squaring them is then represented algebraically as (a+b) ^ 2 == a^2 + b^2 + 2ab which can then be easily combined:

79^2 = 49, 126, 81 => 6241 a == 7, a^2 == 49

b == 9, b^2 == 81

2ab == 279 = 126

combination == (a^2+2ab+b^2)

from 81 take 1

add '8' to 2ab == 134, take 4

add '13' to 49 == 62

answer == 6241