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A280408 Irregular triangle read by rows listing the prime numbers that appear from the trajectory of n in Collatz Problem. 3
2, 2, 3, 5, 2, 2, 5, 2, 3, 5, 2, 7, 11, 17, 13, 5, 2, 2, 7, 11, 17, 13, 5, 2, 5, 2, 11, 17, 13, 5, 2, 3, 5, 2, 13, 5, 2, 7, 11, 17, 13, 5, 2, 23, 53, 5, 2, 2, 17, 13, 5, 2, 7, 11, 17, 13, 5, 2, 19, 29, 11, 17, 13, 5, 2, 5, 2, 2, 11, 17, 13, 5, 2, 23, 53, 5, 2, 3, 5, 2, 19, 29, 11, 17, 13, 5, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..87.

EXAMPLE

The irregular array a(n,k) starts:

n\k   1   2   3   4   5   6

...

1:    2

2:    2

3:    3   5   2

4:    2

5:    5   2

6:    3   5   2

7:    7  11  17  13   5   2

8:    2

9:    7  11  17  13   5   2

10:   5  2

11:  11  17  13   5   2

12:   3   5   2

13:  13   5   2

14:   7  11  17  13   5   2

15:  23  53   5   2

MATHEMATICA

Table[Select[NestWhileList[If[EvenQ@ #, #/2, 3 # + 1] &, n, # > 1 &], PrimeQ], {n, 2, 30}] // Flatten (* Michael De Vlieger, Jan 02 2017 *)

PROG

(Python)

from sympy import isprime

def a(n):

    if n==1: return [2]

    l=[n, ]

    while True:

        if n%2==0: n/=2

        else: n = 3*n + 1

        l+=[n, ]

        if n<2: break

    return list(filter(lambda i: isprime(i), l))

for n in range(1, 21): print a(n) # Indranil Ghosh, Apr 14 2017

CROSSREFS

Cf. A070165, A280409.

Sequence in context: A329792 A058256 A140183 * A130725 A256015 A138117

Adjacent sequences:  A280405 A280406 A280407 * A280409 A280410 A280411

KEYWORD

tabf,nonn,changed

AUTHOR

Matthew Campbell, Jan 02 2017

STATUS

approved

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Last modified December 13 06:26 EST 2019. Contains 329968 sequences. (Running on oeis4.)