Write in terms of factorials: `3xx6xx9xx12xx15`

Write in terms of factorials: 6xx8xx7xx9

Write in terms of factorials: 6xx7xx12xx10

Write in terms of factorials: 5xx10xx15xx20

Find the factorials of 6xx7xx8xx9xx5

Find the factorials of 3xx8xx5

Find the factorials of 15xx8xx6

Find the factorials of 6xx20xx8xx42

Find the factorials of 10xx12xx6

Find the sum to n terms of the series : 1xx2xx3 + 2xx3xx4 + 3xx4xx5 + ...

Finds the sum of first n terms of the series 3/(1^2xx2^2)+5/(2^2xx3^2)+7/(3^2xx4^2)+...... and hence deduce the sum of infinity.