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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A076461 Sum of squares of numbers that can be written as t*n + u*(n+1) for nonnegative integers t,u in exactly two ways. 2
13, 571, 5306, 26470, 93455, 264313, 640276, 1383276, 2736465, 5047735, 8796238, 14621906, 23357971, 36066485, 54076840, 79027288, 112909461, 158115891, 217490530, 294382270, 392701463, 516979441, 672431036, 865020100, 1101528025, 1389625263, 1737945846, 2156164906 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

REFERENCES

Fred. Schuh, Vragen betreffende een onbepaalde vergelijking, Nieuw Tijdschrift voor Wiskunde, 52 (1964-1965) 193-198.

LINKS

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

FORMULA

a(n) = n*(n+1)*(25*n^4+26*n^3-6*n^2-7*n+1)/6.

G.f.: x*(13+480*x+1582*x^2+864*x^3+61*x^4)/(1-x)^7.

MAPLE

seq(1/6*n*(n+1)*(25*n^4+26*n^3-6*n^2-7*n+1), n=1..30);

MATHEMATICA

CoefficientList[Series[(13 + 480 x + 1582 x^2 + 864 x^3 + 61 x^4)/(1 - x)^7, {x, 0, 50}], x] (* Vincenzo Librandi, Dec 30 2013 *)

PROG

(MAGMA) [n*(n+1)*(25*n^4+26*n^3-6*n^2-7*n+1)/6: n in [1..50]]; // Vincenzo Librandi, Dec 30 2013

CROSSREFS

Cf. A076389, A076460-A076465.

Sequence in context: A265503 A050286 A096761 * A168601 A142210 A109875

Adjacent sequences:  A076458 A076459 A076460 * A076462 A076463 A076464

KEYWORD

easy,nonn

AUTHOR

Floor van Lamoen, Oct 13 2002

EXTENSIONS

More terms from Vincenzo Librandi, Dec 30 2013

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 September 20 12:42 EDT 2017. Contains 292271 sequences.