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A349676
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Iterated Pillai's arithmetical function: a(1) = 2, for n >= 2, a(n) = A018804(a(n-1)).
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0
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2, 3, 5, 9, 21, 65, 225, 1365, 14625, 223125, 5630625, 376228125, 38759765625, 3471767578125, 934835712890625, 497199051298828125, 613613372156103515625, 2538878964828409423828125, 25280374785655551910400390625, 243473923053903449878692626953125, 9202204429788304689688510894775390625
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OFFSET
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1,1
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LINKS
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FORMULA
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a(1) = 2, a(n) = A018804(a(n-1)) for n >= 2.
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EXAMPLE
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a(5) = f(f(f(f(a(1))))) = 21. Here f represents A018804.
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MATHEMATICA
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f[p_, e_] := (e*(p - 1)/p + 1) * p^e; pil[n_] := Times @@ f @@@ FactorInteger[n]; NestList[pil, 2, 20] (* Amiram Eldar, Nov 24 2021 *)
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PROG
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(PARI) f(n) = sumdiv(n, d, n*eulerphi(d)/d); \\ A018804
lista(nn) = my(a = 2); for (n=1, nn, print1(a, ", "); a = f(a); ); \\ Michel Marcus, Nov 24 2021
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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