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

Author

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

Keywords

• easy
• nonn

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).

Crossrefs

Cf. A000217, A051936, A101881, A101882.

Programs

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 *)

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]