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A030653 n^3*a(n) is number of circles in complex projective plane tangent to three smooth curves of degree n in general position. 1
4, 23, 60, 121, 212, 339, 508, 725, 996, 1327, 1724, 2193, 2740, 3371, 4092, 4909, 5828, 6855, 7996, 9257, 10644, 12163, 13820, 15621, 17572, 19679, 21948, 24385, 26996, 29787, 32764, 35933, 39300, 42871, 46652, 50649, 54868, 59315 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

REFERENCES

See formula for enumeration of contacts in Fulton-Kleiman-MacPherson (pp. 156-196 of Lect. Notes Math. n.997).

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Index to sequences with linear recurrences with constant coefficients, signature (4,-6,4,-1).

FORMULA

a(n)=n^3+3*n^2+3*n-3.

G.f.: x*(4+7*x-8*x^2+3*x^3)/(1-x)^4. [Colin Barker, Sep 03 2012]

PROG

(MAGMA) [n^3+3*n^2+3*n-3: n in [1..45]]; // Vincenzo Librandi, Jun 30 2011

CROSSREFS

Sequence in context: A106684 A239624 A179628 * A085505 A065972 A132112

Adjacent sequences:  A030650 A030651 A030652 * A030654 A030655 A030656

KEYWORD

nonn,nice,easy

AUTHOR

Paolo Dominici (pl.dm(AT)libero.it)

STATUS

approved

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Last modified November 21 11:17 EST 2014. Contains 249777 sequences.