login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual Appeal: Please make a donation (tax deductible in USA) to keep the OEIS running. Over 5000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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 entries for 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]

MATHEMATICA

LinearRecurrence[{4, -6, 4, -1}, {4, 23, 60, 121}, 40] (* Harvey P. Dale, Nov 29 2014 *)

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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified December 7 11:15 EST 2016. Contains 278872 sequences.