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 A165559 Product of the arithmetic derivatives from 2 to n. 2
 1, 1, 4, 4, 20, 20, 240, 1440, 10080, 10080, 161280, 161280, 1451520, 11612160, 371589120, 371589120, 7803371520, 7803371520, 187280916480, 1872809164800, 24346519142400, 24346519142400, 1071246842265600, 10712468422656000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,3 LINKS FORMULA a(n) = Product_{k=2..n} A003415(k). From Amiram Eldar, Nov 15 2020: (Start) Sum_{n>=2} 1/a(n) = A190144. Sum_{n>=2} (-1)^n/a(n) = A209873. (End) MAPLE P:= proc(p) local a, b, m, n, i, ok, pd, t1, t2, t3; a:=0; pd:=1; for n from 2 by 1 to p do b:=1000000000039; ok:=0; if n<=1 then a:=0; ok:=1; fi; if isprime(n) then a:=1; ok:=1; fi; if ok=0 then t1:=ifactor(b*n); m:=nops(t1); t2:=0; for i from 1 to m do t3:=op(i, t1); if nops(t3)=1 then t2:=t2+1/op(t3); else t2:=t2+op(2, t3)/op(op(1, t3)); fi; od; t2:=t2-1/b; a:=n*t2; fi; pd:=pd*a; print(pd); od; end: P(100); # Alternative program A003415 := proc(n) local pfs ; if n <= 1 then 0 ; else pfs := ifactors(n)[2] ; n*add(op(2, p)/op(1, p), p=pfs) ; fi; end: A165559 := proc(n) mul( A003415(k), k=2..n) ; end: seq( A165559(n), n=2..30) ; # R. J. Mathar, Sep 26 2009 MATHEMATICA d[0] = d[1] = 0; d[n_] := d[n] = n*Total[Apply[#2/#1 &, FactorInteger[n], {1}]]; a[n_] := Product[d[k], {k, 2, n}]; Table[a[n], {n, 2, 25}] (* Jean-François Alcover, Feb 21 2014 *) CROSSREFS Cf. A003415, A190144, A209873. Sequence in context: A261568 A087213 A117857 * A180967 A231884 A052923 Adjacent sequences: A165556 A165557 A165558 * A165560 A165561 A165562 KEYWORD easy,nonn AUTHOR Paolo P. Lava and Giorgio Balzarotti, Sep 22 2009 EXTENSIONS Entries checked by R. J. Mathar, Sep 26 2009 STATUS approved

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Last modified December 1 23:44 EST 2022. Contains 358485 sequences. (Running on oeis4.)