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A076307 a(n) = n+min(2*floor(a(n-1)/2), 3*floor(a(n-1)/3)) for n > 1, a(1)=1. 0
1, 2, 3, 6, 11, 15, 21, 28, 36, 46, 56, 66, 79, 92, 105, 120, 137, 153, 171, 190, 210, 232, 254, 276, 301, 326, 351, 378, 407, 435, 465, 496, 528, 562, 596, 630, 667, 704, 741, 780, 821, 861, 903, 946, 990, 1036, 1082, 1128, 1177, 1226, 1275, 1326, 1379, 1431 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..54.

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

FORMULA

a(n) = n*(n-1)/2 + b(n) where b repeats the period (1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0) of length 12.

a(n) = +2*a(n-1) -a(n-2) +a(n-12) -2*a(n-13) +a(n-14).

G.f.: -x*(1+2*x^4-x^5+2*x^6+x^7+x^8+2*x^9+2*x^12+2*x^3) / ( (1+x) *(1+x^2) *(1+x+x^2) *(x^2-x+1) *(x^4-x^2+1) *(x-1)^3 ).

MATHEMATICA

LinearRecurrence[{2, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -2, 1}, {1, 2, 3, 6, 11, 15, 21, 28, 36, 46, 56, 66, 79, 92}, 60] (* Harvey P. Dale, Nov 29 2013 *)

PROG

(MAGMA) [ n eq 1 select 1 else n+Min(2*Floor(Self(n-1)/2), 3*Floor(Self(n-1)/3)) : n in [1..60] ]; // Klaus Brockhaus, Dec 03 2010

(MAGMA) b:=func< n | [1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0][(n mod 12)+1] >; [ n*(n-1)/2+b(n-1): n in [1..60] ]; // Klaus Brockhaus, Dec 03 2010

CROSSREFS

Sequence in context: A090304 A005211 A298702 * A102990 A138519 A138520

Adjacent sequences:  A076304 A076305 A076306 * A076308 A076309 A076310

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Nov 06 2002

STATUS

approved

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Last modified January 17 12:33 EST 2020. Contains 330958 sequences. (Running on oeis4.)