OFFSET
0,3
COMMENTS
Position of 6 occurs every 2^(n-1) + 1 for n > 0.
Position of 18 appears to occur according to the tetranacci numbers (cf. A000288): 4, 7, 13, 25, 49, ...
REFERENCES
S. M. Ulam, On some mathematical problems connected with patterns of growth of figures, pp. 215-224 of R. E. Bellman, ed., Mathematical Problems in the Biological Sciences, Proc. Sympos. Applied Math., Vol. 14, Amer. Math. Soc., 1962 (see Example 6, page 224).
EXAMPLE
When written as a triangle:
0
1
6
6 18
6 30 18 54
6 30 30 78 18 90 54 150
6 30 30 78 30 126 78 222 18 90 90 234 54 246 150 390
...
CROSSREFS
KEYWORD
nonn
AUTHOR
Cody B Duncan, Jun 23 2020
STATUS
approved