19845k = 3*3*3*3*5*7*7k = 34*51*72k
by a value that will make it
a perfect cube, we much choose a value that will cause
every factor to have an exponent which is a multiple of 3.
The 34 must be multiplied by 32 so it
will become 36
The 51 must be multiplied by 52 so it
will become 53
The 72 must be multiplied by 71 so it
will become 73
So we must multiply 34*51*72 by
32*52*71
So k = 32*52*71 = 9*25*7 = 1575
So the smallest possible positive integer value of k is 1575
Checking:
19845*1575 = 31255875 = 315³
Edwin