a(n) is the number of words of length n over an alphabet of size 3 that are in standard order and which have the property that every letter that appears in the word is repeated.
A278988
a(n) is the number of words of length n over an alphabet of size 3 that are in standard order and which have the property that every letter that appears in the word is repeated.
Terms
- a(0) =0a(1) =0a(2) =1a(3) =1a(4) =4a(5) =11a(6) =41a(7) =162a(8) =610a(9) =2165a(10) =7327a(11) =23948a(12) =76352a(13) =239175a(14) =739909a(15) =2268710a(16) =6912430a(17) =20966441a(18) =63390587a(19) =191220048a(20) =575888044a(21) =1732382363a(22) =5207108161a(23) =15642295562a(24) =46970926394a(25) =141005053341a(26) =423208097431
External references
- oeis: A278988