This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A108489 Expansion of 1/sqrt(1-2x-5x^2-6x^3+9x^4). 0
 1, 1, 4, 13, 37, 130, 427, 1441, 4954, 16987, 58843, 204610, 713893, 2500183, 8778478, 30898309, 108987427, 385136680, 1363252603, 4832572951, 17153677534, 60961916965, 216887253409, 772400234074, 2753261490919, 9822393082513 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS In general, sum{k=0..n, C(n-k,k)^2*a^k*b^(n-k)} has expansion 1/sqrt(1-2bx-(2ab-b^2)x^2-2a*b^2*x^3+(ab)^2*x^4). LINKS FORMULA a(n)=sum{k=0..n, C(n-k, k)^2*3^k} CROSSREFS Cf. A108484. Sequence in context: A077842 A067633 A091874 * A155375 A155307 A155344 Adjacent sequences:  A108486 A108487 A108488 * A108490 A108491 A108492 KEYWORD easy,nonn AUTHOR Paul Barry, Jun 04 2005 STATUS approved

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

Content is available under The OEIS End-User License Agreement .