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A177501
The number of entries in row n of table A174625 which are multiples of n.
2
1, 1, 1, 1, 2, 1, 3, 2, 3, 2, 5, 2, 6, 4, 4, 5, 8, 4, 9, 4, 6, 6, 11, 4, 10, 8, 10, 7, 14, 6, 15, 11, 10, 12, 12, 8, 18, 12, 13, 10, 20, 8, 21, 12, 15, 16, 23, 13, 21, 16, 19, 15, 26, 15, 21, 15, 21, 22, 29, 13, 30, 26, 21, 24, 25, 18, 33, 21, 25, 19, 35, 18, 36, 26, 24, 23, 31, 19, 39, 23
OFFSET
1,5
COMMENTS
n is prime iff a(n) = floor(n/2).
For n >= 2, a(n) is the number of integers of the form binomial(n-k-1, k-1)/k, k=1..floor(n/2). - Vladimir Shevelev, Aug 18 2013
LINKS
FORMULA
For n >= 2, a(n) >= A000010(n)/2. Equality holds when n is odd prime.
EXAMPLE
In the fifth row, 5 and 5 are both multiples of 5, so a(5)=2.
MATHEMATICA
p[0]:=0; p[1]:=2; p[n_]:=p[n]=Expand[p[n-1] +x p[n-2]+1]; Flatten[{1, Table[Count[CoefficientList[p[n]/(n+1) , x], _Integer], {n, 50}]}] (* Peter J. C. Moses, Aug 20 2013 *)
CROSSREFS
Sequence in context: A104481 A078709 A023022 * A330926 A323273 A100677
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, May 10 2010
EXTENSIONS
Definition shortened, more terms added by R. J. Mathar, Nov 01 2010
STATUS
approved