A258098 3x + 1 sequence starting at 79.

79, 238, 119, 358, 179, 538, 269, 808, 404, 202, 101, 304, 152, 76, 38, 19, 58, 29, 88, 44, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1, 4

Offset: 0

Author

Alonso del Arte, May 19 2015

Keywords

• nonn
• easy

Examples

			79 is odd, so it's followed by 3 * 79 + 1 = 238.
238 is even, so it's followed by 238/2 = 119.
		

Crossrefs

Cf. A006370, A033478, A008874, A258056.

Row 79 of A347270.

Programs

Magma

[n eq 1 select 79 else IsOdd(Self(n-1)) select 3*Self(n-1)+1 else Self(n-1) div 2: n in [1..100]]; // Vincenzo Librandi, May 27 2015

Mathematica

NestList[If[EvenQ[#], #/2, 3# + 1] &, 79, 100]

Scala

def collatz(n: Int): Int = n % 2 match {
  case 0 => n / 2
  case _ => 3 * n + 1
}
def collatzSeq(n: Int): LazyList[Int] = LazyList.iterate(n)(collatz)
collatzSeq(79).take(100).toList // Alonso del Arte, Apr 26 2020

Formula

a(0) = 79; a(n) = 3*a(n - 1) + 1 if a(n - 1) is odd, a(n) = a(n - 1)/2 otherwise.