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A245671 3*x + 1 sequence starting at 1729. 5
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 (list; graph; refs; listen; history; text; internal format)
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

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

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: A018850 A062924 A130859 * A154716 A154728 A286217

Adjacent sequences:  A245668 A245669 A245670 * A245672 A245673 A245674

KEYWORD

nonn,easy

AUTHOR

Vincenzo Librandi, Jul 29 2014

STATUS

approved

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Last modified July 17 23:21 EDT 2019. Contains 325109 sequences. (Running on oeis4.)