https://projecteuler.net/problem=20
n! means n × (n − 1) × ... × 3 × 2 × 1
For example, 10! = 10 × 9 × ... × 3 × 2 × 1 = 3628800, and the sum of the digits in the number 10! is 3 + 6 + 2 + 8 + 8 + 0 + 0 = 27.
Find the sum of the digits in the number 100!
const { Stack } = require('@hypercubed/f-flat');
const f = new Stack();
f.eval(`
core: rcl use
math: rcl use
160 set-precision
`).stack;
We create a new f-flat stack environment, bring the math and core modules into sopce, and set the precision to 200 places (100! is a 157 digit value).
f.eval(`
( 100 ! 0 [ swap 10 divrem ] 160 times ) sum
`).stack[0].valueOf();
Inside an list, calulate the factorial of 100. Then divrem by 10 (returns the result and remainder of integer division) 200 times to retreive each digit. Then sum the list.
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