login

Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.

G.f.: WL(-x)*WU(x), where WL, WU are respectively the characteristic functions of the lower (A000201) and upper (A001950) Wythoff sequences.
4

%I #8 Mar 30 2012 18:37:22

%S 1,-1,1,-2,1,0,1,1,0,0,1,-1,1,1,1,2,-1,1,1,0,1,-1,1,1,0,0,1,-1,1,-2,1,

%T 0,1,-1,1,-2,1,-3,1,-1,1,0,1,-1,1,-2,1,0,1,1,0,0,1,-1,1,-2,1,0,1,-1,1,

%U -2,1,-3,1,-1,2,-2,1,-3,1,-4,1,-2,1,-1,2

%N G.f.: WL(-x)*WU(x), where WL, WU are respectively the characteristic functions of the lower (A000201) and upper (A001950) Wythoff sequences.

%C Mentioned in a posting by Paul D. Hanna to the Sequence Fans Mailing List, Dec 28 2010.

%F It appears that the records for positive integers occur at positions A059973(4n+1)-2 and A059973(4n+2)-2, while the records for negative integers occur at positions A059973(4n-1)-1 and A059973(4n)-1;

%F that is, the records seem to obey the following rule:

%F * a(A059973(4n+1)-2) = 2n-1 for n>1,

%F * a(A059973(4n+2)-2) = 2n for n>=1,

%F * a(A059973(4n-1)-1) = -(2n-1) for n>=1,

%F * a(A059973(4n)-1) = -(2n) for n>=1;

%F see A183555 and A183556.

%e WL(x) = 1 + x + x^3 + x^4 + x^6 + x^8 + x^9 + x^11 + x^12 +...+ x^[n*phi] + ...

%e WU(x) = 1 + x^2 + x^5 + x^7 + x^10 + x^13 + x^15 + x^18 +...+ x^[n*(phi+1)] + ...

%e G.f.: WL(-x)*WU(x) = 1 - x + x^2 - 2*x^3 + x^4 + x^6 + x^7 + x^10 - x^11 + x^12 + x^13 + x^14 + 2*x^15 - x^16 +...+ a(n)*x^n +...

%e Positions of records for positive coefficients (A183555) in WL(-x)*WU(x) begin:

%e 1: 0

%e 2: 15

%e 3: 159

%e 4: 303

%e 5: 2887

%e 6: 5471

%e 7: 51839

%e 8: 98207

%e 9: 930247

%e 10: 1762287

%e ...

%e Positions of records for negative coefficients (A183556) in WL(-x)*WU(x) begin:

%e -1: 1

%e -2: 3

%e -3: 37

%e -4: 71

%e -5: 681

%e -6: 1291

%e -7: 12237

%e -8: 23183

%e -9: 219601

%e -10: 416019

%e ...

%e Now compare the above positions to A059973:

%e [1,1, 2,4, 9,17, 38,72, 161,305, 682,1292, 2889,5473, 12238,23184, 51841,98209, 219602,416020, 930249,1762289, ...].

%o (PARI) {a(n)=local(phi=(1+sqrt(5))/2,WL=sum(m=0,ceil(n/phi),(-x)^floor(m*phi))+x*O(x^n),WU=sum(m=0,ceil(n/(phi+1)),x^floor(m*(phi+1)))+x*O(x^n));polcoeff(WL*WU,n)}

%Y Cf. A000201, A001950; A183555, A183556, A183557; A059973.

%K sign

%O 0,4

%A _N. J. A. Sloane_, Jan 05 2011

%E Formula, examples, and program added by _Paul D. Hanna_, Jan 07 2011