A091975 a(1) = 1; for n>1, a(n) = largest integer k such that the word a(1)a(2)...a(n-1) is of is of the form xy^(k_1)Y^(k_2)y^(k_3)Y^(k_4)...y^(k_(m-1))Y^(k_m) where y has positive length and Y=reverse(y) and k_1+k_2+k_3+...+k_m = k.

1, 1, 2, 1, 1, 2, 2, 2, 3, 1, 1, 2, 1, 1, 2, 2, 2, 3, 2, 1, 1, 2, 2, 2, 3, 2, 2, 2, 3, 2, 2, 2, 3, 3, 2, 2, 2, 4, 1, 1, 2, 1, 1, 2, 2, 2, 3, 1, 1, 2, 1, 1, 2, 2, 2, 3, 2, 1, 1, 2, 2, 2, 3, 2, 2, 2, 3, 2, 2, 2, 3, 3, 2, 2, 2, 4, 2, 1, 1, 2, 2, 2, 3, 1, 1, 2, 1, 1, 2, 2, 2, 3, 1, 1, 2, 2, 2, 3, 2, 1, 1, 2, 2, 2, 3

Offset: 1

Author

J. Taylor (integersfan(AT)yahoo.com), Mar 15 2004

Keywords

• nonn

Comments

Here ^ denotes concatenation. This is similar to Gijswijt's sequence A090822 except that the 'y' block still counts when reversed. Thus 2 1 1 2 counts as the 2 blocks (21)(12)

Links

• Michael S. Branicky, Table of n, a(n) for n = 1..10000
• F. J. van de Bult, D. C. Gijswijt, J. P. Linderman, N. J. A. Sloane and Allan Wilks, A Slow-Growing Sequence Defined by an Unusual Recurrence, J. Integer Sequences, Vol. 10 (2007), #07.1.2.
• F. J. van de Bult, D. C. Gijswijt, J. P. Linderman, N. J. A. Sloane and Allan Wilks, A Slow-Growing Sequence Defined by an Unusual Recurrence [pdf, ps].
• Index entries for sequences related to Gijswijt's sequence

Crossrefs

Cf. A090822, A091976, A092331-A092335.

Programs

Python

def k(s):
    maxk = 1
    for m in range(1, len(s)+1):
        i, y, kk = 1, s[-m:], len(s)//m
        if kk <= maxk: return maxk
        yY = [y, y[::-1]]
        while s[-(i+1)*m:-i*m] in yY: i += 1
        maxk = max(maxk, i)
def aupton(terms):
    alst = [1]
    for n in range(2, terms+1):
        alst.append(k(alst))
    return alst
print(aupton(105)) # Michael S. Branicky, Nov 05 2023