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 A105075 a(1) = 1; a(n) = Sum_{k=1..n-1} phi(a(k)*a(n-k)), where phi(m) is the totient function. 0
 1, 1, 2, 3, 6, 10, 16, 38, 80, 160, 328, 752, 1712, 4000, 8736, 16940, 34816, 83904, 178304, 433408, 1031552, 2601600, 5193984, 11318272, 26631680, 62674688, 160582656, 336680960, 715578368, 1829193728, 4724027392, 11004676992 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS MAPLE with(numtheory): a:=array(1..100): a[1]:=1: for n from 1 to 49 do a[n+1]:=sum(phi(a[k]*a[n+1-k]), k=1..n) od: for i from 1 to 50 do printf(`%d, `, a[i]) od: # James A. Sellers, Apr 09 2005 MATHEMATICA a[1] = 1; a[n_] := Sum[ EulerPhi[ a[k] a[n - k]], {k, n - 1}]; Table[ a[n], {n, 32}] (* Robert G. Wilson v, Apr 09 2005 *) CROSSREFS Cf. A000010. Sequence in context: A198200 A294444 A066895 * A140669 A001636 A036588 Adjacent sequences:  A105072 A105073 A105074 * A105076 A105077 A105078 KEYWORD nonn AUTHOR Leroy Quet, Apr 06 2005 EXTENSIONS More terms from James A. Sellers and Robert G. Wilson v, Apr 09 2005 STATUS approved

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Last modified July 26 01:20 EDT 2021. Contains 346294 sequences. (Running on oeis4.)