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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 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.)