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A106466 Interleave 1,2,3,.. with 1,1,2,2,3,3,... 4
1, 1, 2, 1, 3, 2, 4, 2, 5, 3, 6, 3, 7, 4, 8, 4, 9, 5, 10, 5, 11, 6, 12, 6, 13, 7, 14, 7, 15, 8, 16, 8, 17, 9, 18, 9, 19, 10, 20, 10, 21, 11, 22, 11, 23, 12, 24, 12, 25, 13, 26, 13, 27, 14, 28, 14, 29, 15, 30, 15, 31, 16, 32, 16, 33, 17, 34, 17, 35, 18, 36 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Diagonal sums of A106465.

LINKS

Table of n, a(n) for n=0..70.

Index entries for linear recurrences with constant coefficients, signature (0,1,0,1,0,-1).

FORMULA

G.f.: (1+x+x^2)/((1+x^2)(1-x^2)^2); a(n)=a(n-2)+a(n-4)-a(n-6); a(n)=sum{k=0..floor(n/2), gcd(n-k+1, k+1) mod 2};

a(n) = sin(Pi*n/2)/4+(n+2)*(-1)^n/8+3(n+2)/8; a(n) = 0^n + sum{k=0..n-1, if(k=floor((n-1)/2) or k=floor(n/2),1,0)*floor((k+2)/2)}. - Paul Barry, Nov 22 2009

Also, a(n)=((3+(-1)^n)*(n+2)-i*(i^n-(-i)^n))/8, where I is the imaginary unit. - Bruno Berselli, Feb 22 2010

MATHEMATICA

With[{no=36}, Riffle[Range[no], Sort[Join[Range[no/2], Range[no/2]]]]]  (* Harvey P. Dale, Feb 20 2011 *)

CROSSREFS

Sequence in context: A214270 A289440 A290636 * A130722 A147541 A024162

Adjacent sequences:  A106463 A106464 A106465 * A106467 A106468 A106469

KEYWORD

easy,nonn

AUTHOR

Paul Barry, May 03 2005

STATUS

approved

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Last modified April 25 16:59 EDT 2019. Contains 322461 sequences. (Running on oeis4.)