A101883 Write four numbers, skip one, write four, skip two, write four, skip three... and so on.

1, 2, 3, 4, 6, 7, 8, 9, 12, 13, 14, 15, 19, 20, 21, 22, 27, 28, 29, 30, 36, 37, 38, 39, 46, 47, 48, 49, 57, 58, 59, 60, 69, 70, 71, 72, 82, 83, 84, 85, 96, 97, 98, 99, 111, 112, 113, 114, 127, 128, 129, 130, 144, 145, 146, 147, 162, 163, 164, 165, 181, 182, 183, 184, 201

Offset

1,2

Comments

Union of A051936, A051936+1, A051936+2, and A051936+3. - Ivan Neretin, Aug 03 2016

First terms of the four repeated terms belong to A051936. - Michael De Vlieger, Aug 03 2016

Links

Ivan Neretin, Table of n, a(n) for n = 1..10000

Index entries for linear recurrences with constant coefficients, signature (1,0,0,2,-2,0,0,-1,1).

Formula

G.f.: x*(1+x+x^2+x^3-x^5-x^6-x^7)/ ((1+x)^2 * (x^2+1)^2 * (1-x)^3). [Maksym Voznyy (voznyy(AT)mail.ru), Aug 11 2009; checked and corrected by R. J. Mathar, Sep 16 2009]

Mathematica

LinearRecurrence[{1, 0, 0, 2, -2, 0, 0, -1, 1}, {1, 2, 3, 4, 6, 7, 8, 9, 12}, 80] (* or *) Rest[CoefficientList[Series[x*(1+x+x^2+x^3-x^5-x^6-x^7)/((1+x)^2(x^2+1)^2(1-x)^3), {x, 0, 80}], x]](* Harvey P. Dale, Jan 19 2016 *)
Table[Range[#, # + 3] &[n (n + 1)/2 - 9], {n, 4, 20}] // Flatten (* Michael De Vlieger, Aug 03 2016 *)

Crossrefs

Cf. A000217, A051936, A101881, A101882.

Sequence in context: A239015 A030706 A285986 * A236207 A375018 A225837

Adjacent sequences: A101880 A101881 A101882 * A101884 A101885 A101886

Keyword

easy,nonn

Author

Candace Mills (scorpiocand(AT)yahoo.com), Dec 19 2004

Status

approved