func Euler041() int {
//process 7 digit pandigitals
p7d := make([]int, 0, 5040) //7!
for v := range utils.Perm(utils.Numerals[1:8]) {
n, _ := strconv.Atoi(v)
p7d = append(p7d, n)
}
sort.Sort(sort.Reverse(sort.IntSlice(p7d)))
for i := 0; i < 5040; i++ {
if utils.IsPrime(p7d[i]) {
return p7d[i]
}
}
//process 4 digit pandigitals
p4d := make([]int, 0, 24) //4!
for v := range utils.Perm(utils.Numerals[1:5]) {
n, _ := strconv.Atoi(v)
p4d = append(p4d, n)
}
sort.Sort(sort.Reverse(sort.IntSlice(p4d)))
for i := 0; i < 5040; i++ {
if utils.IsPrime(p4d[i]) {
return p4d[i]
}
}
return -1
}
func GetFactors(n int) (fSlice []uint64) {
if utils.IsPrime(n) {
return []uint64{uint64(n)}
}
un := uint64(n)
for _, v := range pCache {
if un%v == 0 {
fSlice = append(fSlice, v)
}
}
return fSlice
}
func Euler027(absLimit int) int {
maxA, maxB, maxN := 0, 0, 0
for a := -absLimit; a < absLimit; a++ {
for b := -absLimit; b < absLimit; b++ {
n := 0
for {
if utils.IsPrime(n*n + a*n + b) {
n++
} else {
break
}
}
if n > maxN {
maxA, maxB, maxN = a, b, n
}
}
}
return maxA * maxB
}
func Euler049() int {
pg := primegen.New()
pg.SkipTo(1489) //skip primes with less 4 digits and the example starting prime.
for p := pg.Next(); p < 9999; p = pg.Next() {
seq := make([]uint64, 0, 3)
isPerm := GetPermutations(p)
seq = append(seq, p)
for n := p + 3330; utils.IsPrime(int(n)) && isPerm[n]; n += 3330 {
seq = append(seq, n)
if len(seq) == 3 {
num, _ := strconv.Atoi(fmt.Sprintf("%v%v%v", seq[0], seq[1], seq[2]))
return num
}
}
}
return 0
}
func Euler035() int {
primes := utils.AtkinSieve(1000000)
circulars := make(map[int]bool)
for _, p := range primes {
if circulars[p] {
continue
}
circular := true
rots := rotations(p)
for _, r := range rots {
if !utils.IsPrime(r) {
circular = false
break
}
}
if circular {
for _, r := range rots {
circulars[r] = true
}
}
}
return len(circulars)
}