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 A136223 Column 2 of triangle A136220; also equals column 0 of U^3 = A136236 where U = A136228. 5
 1, 3, 21, 208, 2637, 40731, 742620, 15624420, 372892266, 9959561867, 294465305959, 9551090908795, 337297690543923, 12886076807637021, 529624555043780909, 23305654066781507361, 1093356525580359412557 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS P = A136220 is a triangular matrix where column k of P^3 equals column 0 of P^(3k+3) such that column 0 of P^3 equals column 0 of P shift one place left. LINKS Table of n, a(n) for n=0..16. PROG (PARI) {a(n)=local(P=Mat(1), U, PShR); if(n==0, 1, for(i=0, n+1, PShR=matrix(#P, #P, r, c, if(r>=c, if(r==c, 1, if(c==1, 0, P[r-1, c-1])))); U=P*PShR^2; U=matrix(#P+1, #P+1, r, c, if(r>=c, if(r<#P+1, U[r, c], if(c==1, (P^3)[ #P, 1], (P^(3*c-1))[r-c+1, 1])))); P=matrix(#U, #U, r, c, if(r>=c, if(r<#U, P[r, c], (U^c)[r-c+1, 1])))); P[n+3, 3])} CROSSREFS Cf. A136220 (P), A136228 (U), A136236 (U^3); other columns of P: A136221, A136222, A136224. Sequence in context: A167872 A192314 A242635 * A114469 A097690 A037967 Adjacent sequences: A136220 A136221 A136222 * A136224 A136225 A136226 KEYWORD nonn AUTHOR Paul D. Hanna, Dec 25 2007 STATUS approved

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Last modified October 4 02:45 EDT 2023. Contains 365872 sequences. (Running on oeis4.)