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A229525 Sum of coefficients of the transform ax^2 + (4a/k - b)x + 4a/k^2 + 2b/k + c = 0 for a,b,c = 1,-1,-1, k = 1,2,3... 2
11, 5, 31, 11, 59, 19, 95, 29, 139, 41, 191, 55, 251, 71, 319, 89, 395, 109, 479, 131, 571, 155, 671, 181, 779, 209, 895, 239, 1019, 271, 1151, 305, 1291, 341, 1439, 379, 1595, 419, 1759, 461, 1931, 505, 2111, 551, 2299, 599, 2495, 649, 2699, 701, 2911, 755 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The positive/negative roots of ax^2 + bx + c = 0 combine with the negative/positive roots of (ck^2 - bk + c)x^2 +(2ck - b)x + c = 0 to define a point on the hyperbola kxy + x + y = 0. To shift such points (roots) to the hyperbola’s other line, put the coefficients of these equations into the formula Q = ax^2 + (4a/k - b)x + 4a/k^2 + 2b/k + c = 0. For a,b,c = 1,-1,-1 and k = 1,2,3..., the coefficients given by Q are the sequence 1,5,5; 1,3,1; 1,7/3,1/9... Clearing fractions and summing a+b+c gives the sequence.

The negative of the n-th term is the n+4th term of the c coefficient sequence A229526.

LINKS

Colin Barker, Table of n, a(n) for n = 1..1000

Russell Walsmith, CL-Chemy III: Hyper-Quadratics

Index entries for linear recurrences with constant coefficients, signature (0,3,0,-3,0,1).

FORMULA

ax^2 + (4a/k - b)x + 4a/k^2 + 2b/k + c; a,b,c = 1,-1,-1, k = 1,2,3... n.

a(n) = 3*a(n-2)-3*a(n-4)+a(n-6). G.f.: -x*(x^5-x^4-4*x^3-2*x^2+5*x+11) / ((x-1)^3*(x+1)^3). - Colin Barker, Nov 02 2014

a(n) = -(-5+3*(-1)^n)*(4+6*n+n^2)/8. - Colin Barker, Nov 03 2014

EXAMPLE

For k = 5, the coefficients are 1, 9/5, -11/25. Clearing fractions, 25, 45, -11 and 25 + 45 -11 = 59 = a[5].

PROG

(PARI) Vec(-x*(x^5-x^4-4*x^3-2*x^2+5*x+11)/((x-1)^3*(x+1)^3) + O(x^100)) \\ Colin Barker, Nov 02 2014

CROSSREFS

The a coefficients are A168077, b coefficients are A171621, c coefficients are A229526.

Sequence in context: A168206 A120831 A253254 * A174103 A038319 A002547

Adjacent sequences:  A229522 A229523 A229524 * A229526 A229527 A229528

KEYWORD

nonn,easy

AUTHOR

Russell Walsmith, Sep 26 2013

EXTENSIONS

More terms from Colin Barker, Nov 02 2014

STATUS

approved

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Last modified May 25 03:50 EDT 2019. Contains 323539 sequences. (Running on oeis4.)