0,3

Alois P. Heinz, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (8,-28,56,-70,56,-28,8,-1).

a(n) = n*(11954-29577*n+27640*n^2-12831*n^3+3234*n^4-420*n^5+24*n^6)/24.

G.f.: x*(1+38*x+27*x^2+101*x^3+610*x^4+693*x^5+3570*x^6)/(1-x)^8.

a(0) = 0: no word of length 7 is possible for an empty alphabet.

a(1) = 1: aaaaaaa for alphabet {a}.

a(2) = 46: aaaaaaa, aaaaaab, aaaaaba, aaaaabb, aaaabaa, aaaabab, aaaabba, aaaabbb, aaabaaa, aaabaab, aaababa, aaababb, aaabbaa, aaabbab, aaabbba, aabaaaa, aabaaab, aabaaba, aabaabb, aababaa, aababab, aababba, aabbaaa, aabbaab, aabbaba, abaaaaa, abaaaab, abaaaba, abaaabb, abaabaa, abaabab, abaabba, ababaaa, ababaab, abababa, baaaaaa, baaaaab, baaaaba, baaaabb, baaabaa, baaabab, baaabba, baabaaa, baabaab, baababa, bbbbbbb for alphabet {a,b}.

a:= n-> n*(11954+ (-29577 +(27640 +(-12831+(3234+(-420+24*n)*n) *n) *n) *n) *n)/24:

seq(a(n), n=0..40);

Row n=7 of A213276.

Sequence in context: A296402 A077734 A272184 * A135735 A160285 A111304

Adjacent sequences: A213283 A213284 A213285 * A213287 A213288 A213289

nonn,easy

Alois P. Heinz, Jun 08 2012

approved