A109490
Value of Product[k/sd(k,3),k=1..n], where sd[k,b] is the sum of the digits of k represented in base b.
Original entry on oeis.org
1, 1, 3, 6, 10, 30, 70, 140, 1260, 6300, 23100, 138600, 600600, 2102100, 10510500, 42042000, 142942800, 1286485200, 8147739600, 40738698000, 285170886000, 1568439873000, 7214823415800, 43288940494800, 216444702474000
Offset: 1
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P:= 1: A[1]:= P:
for n from 2 to 100 do
P:= P*n/convert(convert(n,base,3),`+`);
A[n]:= P;
od:
seq(A[i],i=1..100); # Robert Israel, Jan 21 2018
A109491
Value of Product_{k=1..n} sigma(k)/sd(k,2), where sd(k,b) is the sum of the digits of k represented in base b.
Original entry on oeis.org
1, 3, 6, 42, 126, 756, 2016, 30240, 196560, 1769040, 7076160, 99066240, 462309120, 3698472960, 22190837760, 687915970560, 6191243735040, 120729252833280, 804861685555200, 16902095396659200, 180289017564364800
Offset: 1
The divisors of 1-5 are {1}, {1,2}, {1,3}, {1,2,4} and {1,5}, respectively and the base-2 representations of 1-5 are 1,10,11,100,101, so a(5)=(1/1)(3/1)(4/2)(7/1)(6/2)=126.
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p:= 1: A[1]:= 1:
for n from 2 to 50 do
p:= p * numtheory:-sigma(n)/convert(convert(n,base,2),`+`);
A[n]:= p;
od:
seq(A[i],i=1..50); # Robert Israel, Jan 22 2018
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a(n) = prod(k=1, n, sigma(k)/hammingweight(k)); \\ Michel Marcus, Jul 10 2014
Showing 1-2 of 2 results.
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