Substring primes: Difference between revisions

Line 449:

<lang ecmascript>import "/math" for Int

var ~~sdigits~~ = [2, 3, 5, 7] // must begin with a prime digit

var results = [2, 3, 5, 7] // number must begin with a prime digit

var odigits = [3, 7] // other digits must be 3 or 7 as there would be a composite substring otherwise

var results = sdigits.toList

var discarded = []

var tests = 4 // i.e. to obtain ~~sdigits~~ in the first place

var tests = 4 // i.e. to obtain initial results in the first place

// check 2 digit numbers

// check 2 digit numbers or greater

// note that 'results' is a moving feast. If the loop eventually terminates that's all there are.

for (sd in ~~sdigits~~) {

for (r in results) {

for (od in odigits) {

// sd and od must be different otherwise number would be divisible by 11

// the last digit of r and od must be different otherwise number would be divisible by 11

if (sd != od) {

var n = sd * 10 + od

if (Int.isPrime(n)) results.add(n) else discarded.add(n)

tests = tests + 1

}

// check 3 digit numbers or greater

for (r in results.where {|r| r > 7 }) {

for (od in odigits) {

// can exclude twin digits as would be divisible by 11

if ((r % 10) != od) {

var n = 10 * r + od

var n = r * 10 + od

if (Int.isPrime(n)) results.add(n) else discarded.add(n)

tests = tests + 1