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A300479
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Numbers k such that k is the uphi(k)-th composite number, where uphi is the unitary totient function.
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0
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6, 12, 15, 21, 24, 28, 36, 52, 68, 76, 265, 295, 2681, 8104, 21413, 174757, 1302197, 15536176, 20149241, 25873648, 237875719, 358334927
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OFFSET
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1,1
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COMMENTS
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The unitary version of A100410.
No more terms below 10^7.
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LINKS
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Table of n, a(n) for n=1..22.
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FORMULA
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Numbers k, such that k = A002808(A047994(k)).
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EXAMPLE
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12 is a term because uphi(12) = 6 and 12 = A002808(6), the 6th composite.
15 is a term because uphi(15) = 8 and 15 = A002808(8), the 8th composite.
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MATHEMATICA
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uphi[n_] :=(Times @@ (Table[#[[1]]^#[[2]] - 1, {1}] & /@ FactorInteger[n] ))[[1]] ; seqQ[n_] := (n - uphi[n] - 1 == PrimePi[n]); Select[Range[2, 10^7], seqQ]
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PROG
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(PARI) uphi(n) = my(f=factor(n)); prod(i=1, #f~, f[i, 1]^f[1, 2]-1);
isok(k) = k - primepi(k) - 1 == uphi(k); \\ Michel Marcus, Mar 07 2018
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CROSSREFS
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Cf. A000720, A002808, A047994, A100410.
Sequence in context: A106420 A308611 A315619 * A315620 A315621 A315622
Adjacent sequences: A300476 A300477 A300478 * A300480 A300481 A300482
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KEYWORD
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nonn,more
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AUTHOR
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Amiram Eldar, Mar 06 2018
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EXTENSIONS
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a(18)-a(22) from Robert G. Wilson v, Mar 07 2018
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STATUS
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approved
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