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A329263
Irregular triangle read by rows in which row n is the result of iterating the operation f(n) = n/8 if n == 0 (mod 8), otherwise f(n) = 8*(floor(n/8) + n + 1), terminating at the first occurrence of 1.
2
1, 2, 24, 3, 32, 4, 40, 5, 48, 6, 56, 7, 64, 8, 1, 3, 32, 4, 40, 5, 48, 6, 56, 7, 64, 8, 1, 4, 40, 5, 48, 6, 56, 7, 64, 8, 1, 5, 48, 6, 56, 7, 64, 8, 1, 6, 56, 7, 64, 8, 1, 7, 64, 8, 1, 8, 1, 9, 88, 11, 104, 13, 120, 15, 136, 17, 160, 20, 184, 23, 208
OFFSET
1,2
COMMENTS
The operation f(n) can be generalized to C(n,m) = n/m if n == 0 (mod m), m*(floor(n/m) + n + 1) otherwise. The operation for the 3x+1 (Collatz) problem is equivalent to C(n,2) and f(n) = C(n,8).
Conjecture: For any initial value of n >= 1 there is a number k such that f^{k}(n) = 1; in other words, every row of the triangle is finite.
FORMULA
a(n,0) = n, a(n,k + 1) = a(n,k)/8 if a(n,k) == 0 (mod 8), 8*(floor(a(n,k)/8) + a(n,k) + 1) otherwise, for n >= 1.
EXAMPLE
The irregular array a(n,k) starts:
n\k 0 1 2 3 4 5 6 7 8 9 10 11 12 13 ...
1: 1
2: 2 24 3 32 4 40 5 48 6 56 7 64 8 1
3: 3 32 4 40 5 48 6 56 7 64 8 1
4: 4 40 5 48 6 56 7 64 8 1
5: 5 48 6 56 7 64 8 1
6: 6 56 7 64 8 1
7: 7 64 8 1
8: 8 1
9: 9 88 11 104 13 120 15 136 17 160 20 184 23 208 ...
10: 10 96 12 112 14 128 16 2 24 3 32 4 40 5 ...
a(9,100) = 1 and a(10,20) = 1.
PROG
(PARI) collatz8(n)=N=[n]; while(n>1, N=concat(N, n=if(n%8, 8*(floor(n/8)+n+1), n/8))); N
CROSSREFS
Cf. A070165.
Sequence in context: A270562 A100816 A079612 * A227477 A351850 A066585
KEYWORD
nonn,easy,tabf
AUTHOR
Davis Smith, Nov 09 2019
STATUS
approved