OFFSET
1,1
COMMENTS
The transuranic elements Pu=31221132221222112112322211 and Np=1311222113321132211221121332211 are alternating prefixes;
n is suffix of a(2*n - 1) and of a(2*n) in decimal representation.
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..500
J. H. Conway, The weird and wonderful chemistry of audioactive decay, in T. M. Cover and Gopinath, eds., Open Problems in Communication and Computation, Springer, NY 1987, pp. 173-188.
Eric Weisstein's World of Mathematics, Look and Say Sequence
Wikipedia, Look-and-say sequence
PROG
(Haskell)
a215403 n k = a215403_list !! (n-1)
a215403_list = map (foldr (\d v -> 10 * v + d) 0) $
concatMap (\x -> map (x :) [plut', nept']) [4..] where
plut' = [1, 1, 2, 2, 2, 3, 2, 1, 1, 2, 1, 1, 2, 2, 2, 1, 2, 2, 2, 3, 1, 1, 2, 2, 1, 3]
nept' = [1, 1, 2, 2, 3, 3, 1, 2, 1, 1, 2, 2, 1, 1, 2, 2, 3, 1, 1, 2, 3, 3, 1, 1, 2, 2, 2, 1, 1, 3, 1]
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Reinhard Zumkeller, Aug 09 2012
STATUS
approved