Data commit

Task/Circular-primes/Lua/circular-primes.lua

@@ -0,0 +1,27 @@
+-- Circular primes, in Lua, 6/22/2020 db
+local function isprime(n)
+  if n < 2 then return false end
+  if n % 2 == 0 then return n==2 end
+  if n % 3 == 0 then return n==3 end
+  for f = 5, math.sqrt(n), 6 do
+    if n % f == 0 or n % (f+2) == 0 then return false end
+  end
+  return true
+end
+
+local function iscircularprime(p)
+  local n = math.floor(math.log10(p))
+  local m, q = 10^n, p
+  for i = 0, n do
+    if (q < p or not isprime(q)) then return false end
+    q = (q % m) * 10 + math.floor(q / m)
+  end
+  return true
+end
+
+local p, dp, list, N = 2, 1, {}, 19
+while #list < N do
+  if iscircularprime(p) then list[#list+1] = p end
+  p, dp = p + dp, 2
+end
+print(table.concat(list, ", "))