A154448 Permutation of nonnegative integers induced by wreath recursion a=s(b,c), b=s(c,a), c=(c,c), starting from state a, rewriting bits from the second most significant bit toward the least significant end.

0, 1, 3, 2, 7, 6, 4, 5, 14, 15, 13, 12, 8, 9, 10, 11, 28, 29, 30, 31, 27, 26, 24, 25, 16, 17, 18, 19, 20, 21, 22, 23, 56, 57, 58, 59, 60, 61, 62, 63, 54, 55, 53, 52, 48, 49, 50, 51, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 112, 113, 114, 115, 116, 117

Offset: 0

Author

Antti Karttunen, Jan 17 2009

Keywords

• nonn
• base

Comments

This permutation of natural numbers is induced by the first generator of group 2861 mentioned on page 144 of "Classification of groups generated by 3-state automata over a 2-letter alphabet" paper. It can be computed by starting scanning n's binary expansion rightward from the second most significant bit, complementing every bit down to and including A) either the first 0-bit at even distance from the most significant bit or B) the first 1-bit at odd distance from the most significant bit.

Examples

			25 = 11001 in binary, the first zero-bit at odd distance from the msb is immediately at where we start (at the second most significant bit), so we complement it and fix the rest, yielding 10001 (17 in binary), thus a(25)=17.
		

Links

• Antti Karttunen, Table of n, a(n) for n = 0..2047
• Bondarenko, Grigorchuk, Kravchenko, Muntyan, Nekrashevych, Savchuk, and Sunic, Classification of groups generated by 3-state automata over a 2-letter alphabet, arXiv:0803.3555 [math.GR], 2008, p. 144.
• Index entries for sequences that are permutations of the natural numbers

Crossrefs

Inverse: A154447. a(n) = A054429(A154447(A054429(n))). Cf. A072376, A153141-A153142, A154435-A154436, A154439-A154446. Corresponds to A154458 in the group of Catalan bijections.

Programs

R

maxlevel <- 5 # by choice
a <- 1
for(m in 0:maxlevel) {
  for(k in 0:(2^m-1)){
  a[2^(m+1) + 2*k    ] <- 2*a[2^m + k]
  a[2^(m+1) + 2*k + 1] <- 2*a[2^m + k] + 1
  }
  x <- floor(2^(m+2)/3)
  a[2*x    ] <- 2*a[x] + 1
  a[2*x + 1] <- 2*a[x]
}
(a <- c(0, a))
# Yosu Yurramendi, Oct 12 2020

Extensions

Spelling/notation corrections by Charles R Greathouse IV, Mar 18 2010