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 A121775 Triangle, read by rows, defined by: T(n,k) = Sum_{d|n} phi(n/d)*C(d,k) for n>0, k>=0, with T(0,0) = 1. 2
 1, 1, 1, 2, 3, 1, 3, 5, 3, 1, 4, 8, 7, 4, 1, 5, 9, 10, 10, 5, 1, 6, 15, 20, 21, 15, 6, 1, 7, 13, 21, 35, 35, 21, 7, 1, 8, 20, 36, 60, 71, 56, 28, 8, 1, 9, 21, 42, 86, 126, 126, 84, 36, 9, 1, 10, 27, 59, 130, 215, 253, 210, 120, 45, 10, 1, 11, 21, 55, 165, 330, 462, 462, 330, 165, 55 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS For n>0, (1/n)*Sum_{k=0..n} T(n,k)*(c-1)^k = number of n-bead necklaces with c colors: A000031 (c=2), A001867 (c=3), A001868 (c=4), A001869 (c=5), A054625 (c=6), A054626 (c=7), A054627 (c=8), A054628 (c=9), A054629 (c=10). LINKS EXAMPLE Triangle begins: 1; 1, 1; 2, 3, 1; 3, 5, 3, 1; 4, 8, 7, 4, 1; 5, 9, 10, 10, 5, 1; 6, 15, 20, 21, 15, 6, 1; 7, 13, 21, 35, 35, 21, 7, 1; 8, 20, 36, 60, 71, 56, 28, 8, 1; 9, 21, 42, 86, 126, 126, 84, 36, 9, 1; 10, 27, 59, 130, 215, 253, 210, 120, 45, 10, 1; PROG (PARI) T(n, k)=if(n

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Last modified January 23 11:04 EST 2019. Contains 319391 sequences. (Running on oeis4.)