345345 ÷15015=345x1001÷（15x1001）=345x1001÷15÷1001=345÷15=23
1/819+1/2223-1/1197
=1/(9*13*7)+1/(19*13*9)-1/(19*9*7)
=[19+7]/(19*13*9*7)-1/(19*9*7)
=2/(19*9*7)-1/(19*9*7)
=1/1197
(1+2+3+4+5+6+7+6+5+4+3+2+1)÷7777×7777
=1+2+3+4+5+6+7+6+5+4+3+2+1
=(1+2+3+4+5+6)×2+7
=(1+6)×6+7
=49