1,2

a(n)=2 if and only if n-1 is in A079523. - Benoit Cloitre, Mar 10 2003.

Partial sums modulo 4 of the sequence 1, a(1), a(1), a(2), a(2), a(3), a(3), a(4), a(4), a(5), a(5), a(6), a(6), ...- DELEHAM Philippe (kolotoko(AT)wanadoo.fr), Mar 04 2004

To construct the sequence : start with 1 and concatenate 4 -1 = 3 : 1, 3, then change the last term (2 -> 1, 3 ->2 ) gives : 1, 2. Concatenate 1, 2 with 4 -1 = 3, 4 - 2 = 2 : 1, 2, 3, 2 and change the last term : 1, 2, 3, 1. Concatenate 1, 2, 3, 1 with 4 - 1 = 3, 4 - 2 = 2, 4 - 3 = 1, 4 - 1 = 3 : 1, 2, 3, 1, 3, 2, 1, 3 and change the last term : 1, 2, 3, 1, 3, 2, 1, 2 etc.- DELEHAM Philippe (kolotoko(AT)wanadoo.fr), Mar 04 2004

To construct the sequence : start with the Thue-Morse sequence A010060 = 0, 1, 1, 0, 1, 0, 0, 1, ... Then change 0 -> 1, 2, 3, _ and 1 -> 3, 2, 1, _ gives : 1, 2, 3, _, 3, 2, 1, _,3, 2, 1, _, 1, 2, 3, _, 3, 2, 1, _, ...and fill in the successive holes with the successive terms of the sequence itself.- DELEHAM Philippe (kolotoko(AT)wanadoo.fr), Mar 04 2004

To construct the sequence : to insert the number 2 between the A003156(k)-th term and the (1 + A003156(k))-th term of the sequence 1, 3, 1, 3, 1, 3, 1, 3, 1, 3, 1, 3, 1, 3, ...- DELEHAM Philippe (kolotoko(AT)wanadoo.fr), Mar 04 2004

Conjecture. The sequence is formed by the numbers of 1's between every pair of consecutive 2's in A076826. [From Vladimir Shevelev (shevelev(AT)bgu.ac.il), May 31 2009]

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

J. Roberts, Lure of the Integers, Math. Assoc. America, 1992, p. 18.

A. Thue. Ueber unendliche Zeichenreihe. Norske Vid. Selsk. Skr. I. Mat. Nat. Kl. Christiania, 7:1a22, 1906.

Roger L. Bagula, Description of sequence as successive rows of a triangle

S. Kitaev and T. Mansour, Counting the occurrences of generalized patterns....

Author?, Title?

a(n) modulo 2 = A035263(n). a(A036554(n)) = 2. a(A003159(n)) = 1 if n odd. a(A003159(n)) = 3 if n even. a(n) = A033485(n) mod 4. a(n) = 4 - A036585(n-1).- DELEHAM Philippe (kolotoko(AT)wanadoo.fr), Mar 04 2004

a(n) = 2 - A029883(n) = 3 - A036577(n) . - DELEHAM Philippe (kolotoko(AT)wanadoo.fr), Mar 20 2004

For n>=1, we have: 1) a(A108269(n))=A010684(n-1); 2) a(A079523(n))=A010684(n-1); 3) a(A081706(2n))=A010684(n). [From Vladimir Shevelev (shevelev(AT)bgu.ac.il), Jun 22 2009]

Nest[ Flatten[ # /. {1 -> {1, 2, 3}, 2 -> {1, 3}, 3 -> {2}}] &, {1}, 7] (from Robert G. Wilson v (rgwv(AT)rgwv.com), May 07 2005)

(PARI) a(n)=if(n<1|valuation(n, 2)%2, 2, 2+(-1)^subst(Pol(binary(n)), x, 1))

Cf. A001285, A010060.

First differences of A000069.

Equals A036580(n-1) + 1.

Cf. A115384 A159481 A007413 A000120

Sequence in context: A128222 A057039 A135511 this_sequence A072457 A063047 A003270

Adjacent sequences: A007410 A007411 A007412 this_sequence A007414 A007415 A007416

nonn,easy

N. J. A. Sloane (njas(AT)research.att.com).