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A225105
Odd numbers n such that the largest odd term in Collatz(3x+1) trajectory of n is prime.
1
3, 5, 7, 9, 11, 13, 15, 17, 19, 23, 25, 29, 35, 37, 39, 53, 59, 61, 67, 75, 79, 87, 89, 99, 101, 105, 113, 115, 119, 131, 149, 153, 157, 173, 179, 181, 187, 197, 211, 219, 229, 241, 247, 249, 255, 267, 269, 277, 281, 307, 317, 329, 349, 371, 373, 383, 397
OFFSET
1,1
LINKS
EXAMPLE
15 is in the list since highest odd number in Collatz trajectory of 15 is 53, a prime.
MATHEMATICA
Coll[n_]:=NestWhileList[If[EvenQ[#], #/2, 3*# + 1] &, n, #>1&]; t={}; Do[If[PrimeQ[Max[Select[Coll[n], OddQ]]], AppendTo[t, n]], {n, 1, 300, 2}]; t
PROG
(Haskell)
a225105 n = a225105_list !! (n-1)
a225105_list = filter
((== 1) . a010051' . maximum . filter odd . a070165_row) a005408_list
-- Reinhard Zumkeller, Apr 30 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Jayanta Basu, Apr 28 2013
STATUS
approved