Module:Utils: Difference between revisions

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@@ Line 48: / Line 48: @@
 	prec = p.eval_num_arg(prec, 6)
 	return string.format(string.format("%%.%dg", prec), x)
+end
+-- cached list of primes for is_prime
+local primes = {}
+-- returns true if integer n is prime; cannot be used with {{#invoke:}}
+function p.is_prime(n)
+  local cached = primes[n]
+  if cached ~= nil then
+    return cached
+  end
+  for i = 2, math.sqrt(n) do
+    if n % i == 0 then
+      primes[n] = false
+      return false
+    end
+  end
+  primes[n] = true
+  return true
+end
+-- returns prime factorisation of integer n > 2 (with wiki markup for exponents)
+function p.prime_factorization(frame)
+	local args = getArgs(frame)
+	return p._prime_factorization(args[1])
+end
+function p._prime_factorization(n)
+  local factors, powers = {}, {}
+  local new_number = n
+  for i = 2, n do
+    if p.is_prime(i) then
+      if new_number % i == 0 then
+        factors[#factors + 1] = i
+        powers[#factors] = 0
+      end
+      while new_number % i == 0 do
+        powers[#factors] = powers[#factors] + 1
+        new_number = new_number / i
+      end
+      powers[#factors] = factors[#factors] .. "<sup>" .. powers[#factors] .. "</sup>"
+    end
+    if new_number == 1 then
+      break
+    end
+  end
+  return table.concat(powers, " × ")
 end
 return p