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A228871 Odd numbers producing 3 out-of-order odd numbers in the Collatz (3x+1) iteration. 2
3, 227, 14563, 932067, 59652323, 3817748707, 244335917283, 15637498706147, 1000799917193443, 64051194700380387, 4099276460824344803, 262353693492758067427, 16790636383536516315363, 1074600728546337044183267, 68774446626965570827729123 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Sequence A198584 gives the first term of the Collatz sequence having exactly 3 odd numbers. This sequence is the subset of A198584 for which the second odd number is larger than the first. The second odd number is (2^(6*n - 2) - 1)/3, which always occurs as the third term of the sequence.

LINKS

Table of n, a(n) for n=1..15.

EXAMPLE

The number 3 has the Collatz iteration {3, 10, 5, 16, 8, 4, 2, 1}, which has three out-of-order odd numbers {3, 5, 1}.

MATHEMATICA

Table[(2*(2^(6*n - 2) - 1)/3 - 1)/3, {n, 15}]

PROG

(PARI) a(n)=4^(3*n-1)\3*2\3 \\ Charles R Greathouse IV, Mar 11 2017

CROSSREFS

Cf. A198584 (Collatz iterations having 3 odd numbers).

Cf. A228872 (Collatz iterations producing 3 in-order odd numbers).

Sequence in context: A241098 A254157 A131493 * A195500 A099426 A332123

Adjacent sequences:  A228868 A228869 A228870 * A228872 A228873 A228874

KEYWORD

nonn,easy

AUTHOR

T. D. Noe, Sep 12 2013

STATUS

approved

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Last modified June 20 06:23 EDT 2021. Contains 345157 sequences. (Running on oeis4.)