OFFSET
0,6
COMMENTS
See A137743 for more comments.
EXAMPLE
a(4) = # { abcd },
a(5) = # { aabcd, abbcd, abccd, abcdd },
a(6) = # { aaabcd, aabbcd, aabccd, aabcdd, ababcd, abbbcd, abbccd, abbcdd, abcbcd, abcccd, abccdd, abcdcd, abcddd }
PROG
(PARI) A135473(12, 4)
(Python)
def process(s, n, catalog, cache):
....l=len(s)
....if l==n:
........catalog.add(s)
........return
....if s in cache:
........return
....cache.add(s)
....for x in range(l):
........for y in range(x+1, min(x+n-l, l)+1):
............process(s[:y]+s[x:], n, catalog, cache)
def A137744(n):
....catalog=set()
....cache=set()
....process("abcd", n, catalog, cache)
....return len(catalog)
# Bert Dobbelaere, Nov 01 2018
CROSSREFS
KEYWORD
more,nonn
AUTHOR
M. F. Hasler, Feb 10 2008
EXTENSIONS
a(13)-a(19) from Lars Blomberg, Jan 12 2013
a(20)-a(21) from Bert Dobbelaere, Nov 01 2018
a(22)-a(23) from Bert Dobbelaere, Jun 10 2024
STATUS
approved