A101882 Write three numbers, skip one, write three, skip two, write three, skip three... and so on.

1, 2, 3, 5, 6, 7, 10, 11, 12, 16, 17, 18, 23, 24, 25, 31, 32, 33, 40, 41, 42, 50, 51, 52, 61, 62, 63, 73, 74, 75, 86, 87, 88, 100, 101, 102, 115, 116, 117, 131, 132, 133, 148, 149, 150, 166, 167, 168, 185, 186, 187, 205, 206, 207, 226, 227, 228, 248, 249, 250, 271

Offset

1,2

Comments

Union of A052905, A052905+1, and A052905+2. - Ivan Neretin, Aug 03 2016

First terms of the 3 repeated terms belong to A052905. - 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 (1,0,2,-2,0,-1,1).

Formula

G.f.: x*(1+x+x^2-x^4-x^5)/ ((1+x+x^2)^2 * (1-x)^3). [Maksym Voznyy (voznyy(AT)mail.ru), Aug 11 2009; checked and corrected by R. J. Mathar, Sep 16 2009]

Mathematica

Flatten@Table[(n^2 + 5 n - 4)/2 + {0, 1, 2}, {n, 20}] (* Ivan Neretin, Aug 03 2016 *)
Table[Range[#, # + 2] &[(n^2 + 7 n + 2)/2], {n, 0, 20}] // Flatten (* or *)
Rest@ CoefficientList[Series[x (1 + x + x^2 - x^4 - x^5)/((1 + x + x^2)^2 (1 - x)^3), {x, 0, 61}], x] (* Michael De Vlieger, Aug 03 2016 *)
LinearRecurrence[{1, 0, 2, -2, 0, -1, 1}, {1, 2, 3, 5, 6, 7, 10}, 70] (* Harvey P. Dale, Dec 26 2019 *)

Prog

(PARI) a(n)=my(k=n%3); if(k==2, n^2+17*n-2, k==1, n^2+19*n-2, n^2+15*n)/18 \\ Charles R Greathouse IV, Aug 03 2016

Crossrefs

Cf. A000217, A052905, A101881, A101883.

Sequence in context: A295389 A028781 A136149 * A318239 A059266 A336222

Adjacent sequences: A101879 A101880 A101881 * A101883 A101884 A101885

Keyword

easy,nonn

Author

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

Status

approved