OFFSET
0,3
COMMENTS
If n >> 1 the structure looks like a right triangle, which is essentially half of one of the six wedges of the E-toothpick (or snowflake) structure of A161330. The sequence gives the number of E-toothpicks in the structure after n stages. A211976 (the first differences) gives the number added at the n-th stage.
LINKS
FORMULA
a(n) = (((A161330(n+1) - 2)/6) + n)/2.
a(n) = A220478(n)/2. - Omar E. Pol, Feb 19 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Omar E. Pol, Dec 17 2012
STATUS
approved