A245671 3*x + 1 sequence starting at 1729.

1729, 5188, 2594, 1297, 3892, 1946, 973, 2920, 1460, 730, 365, 1096, 548, 274, 137, 412, 206, 103, 310, 155, 466, 233, 700, 350, 175, 526, 263, 790, 395, 1186, 593, 1780, 890, 445, 1336, 668, 334, 167, 502, 251, 754, 377, 1132, 566, 283, 850, 425, 1276, 638

Offset

0,1

Comments

1729 is known as the Hardy-Ramanujan number.

This sequence includes all those starting from the odd numbers: 5, 23, 35, 53, 61, 103, 137, 155, 167, 175, 233, 251, 263, 283, 319, 325, 365, 377, 395, 425, 433, 445, 479, 577, 593, 719, 911, 973, 1079, 1297, 1367, 1619.

Reaches a power of 2 at a(100) = 16. - Alonso del Arte, May 30 2015

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..200

Index entries for sequences related to 3x+1 (or Collatz) problem

Formula

a(0) = 1729, a(n) = 3*a(n-1) + 1 if a(n-1) is odd, a(n) = a(n-1)/2 otherwise. - Alois P. Heinz, Jul 29 2014

Mathematica

NestList[If[EvenQ[#], #/2, 3# + 1] &, 1729, 100]

Prog

(Magma) [n eq 1 select 1729 else IsOdd(Self(n-1)) select 3*Self(n-1)+1 else Self(n-1) div 2: n in [1..100]];

Crossrefs

Row 1729 of A347270.

Cf. A001235.

3*x+1 sequence starting at k: A008884 (k = 27), A008880 (k = 33), A008878 (k = 39), A008883 (k = 51), A008877 (k = 57), A008874 (k = 63), A008876 (k = 81), A008879 (k = 87), A008875 (k = 95), A008873 (k = 97), A008882 (k = 99), this sequence (k = 1729).

Sequence in context: A062924 A350270 A130859 * A154716 A154728 A286217

Adjacent sequences: A245668 A245669 A245670 * A245672 A245673 A245674

Keyword

nonn,easy

Author

Vincenzo Librandi, Jul 29 2014

Status

approved