greatest common divisor / lowest common multiple

gcd.bc

define gcd_(a, b) {
  if (b==0)  return a
  return gcd_(b, a%b)
}

define gcd(a, b) {
  if (a<b)  return gcd_(b, a)
  return gcd_(a, b)
}

define lcm(a, b) {
  return a*b/gcd(a,b)
}

pi@pi400-64:~ $ bc -q gcd.bc powm.bc 
p=3490529510847650949147849619903898133417764638493387843990820577
q=32769132993266709549961988190834461413177642967992942539798288533
n=p*q
phi=(p-1)*(q-1)
gcd(p-1, q-1)
4
powm(2, phi/(2^4), n)
1
powm(2, phi/(2^5), n)
42836191202508728742199299040582900202976222916017767167551870216509\
444518239462186379470569442055101392992293082259601738228702
lcm(21,28)
84

powm() here:
https://gist.github.com/Hermann-SW/aefd972ef795347bd5cc7ec4557a769f