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A292033 Unitary phibonacci numbers: solutions k of the equation uphi(k) = uphi(k-1) + uphi(k-2), where uphi(k) is the unitary totient function (A047994). 6
3, 4, 7, 23, 9179, 244967, 14307856, 24571871, 128199059, 140830367, 401767631, 420567856, 468190439, 525970979, 780768167, 886434647, 1597167647, 4046753951, 4473784823, 5364666167, 5515718207, 11175736336, 14408460167, 18026319712, 20106993887, 20357733131 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The unitary version of A065557. Common terms are 3, 7, 23, 9179, 244967, ... Terms that are not in A065557 are 4, 14307856, 420567856, ...

LINKS

Table of n, a(n) for n=1..26.

EXAMPLE

uphi(14307856) = uphi(14307855) + uphi(14307854) (3366080 = 7102080 + 6264000), so 14307856 is in the sequence.

MATHEMATICA

uphi[n_]:=If[n == 1, 1, (Times@@(Table[#[[1]]^#[[2]]-1, {1}] & /@ FactorInteger[n]))[[1]]]; Select[ Range[3, 10^6], uphi[#] == uphi[#-1] + uphi[#-2] &]

PROG

(PARI) uphi(n) = my(f=factor(n)); prod(i=1, #f~, f[i, 1]^f[i, 2]-1);

isok(n) = uphi(n)==uphi(n-1)+uphi(n-2); \\ Altug Alkan, Sep 08 2017

CROSSREFS

Cf. A047994, A065557.

Sequence in context: A124082 A056655 A332971 * A288501 A288019 A288442

Adjacent sequences:  A292030 A292031 A292032 * A292034 A292035 A292036

KEYWORD

nonn

AUTHOR

Amiram Eldar, Sep 07 2017

EXTENSIONS

a(18)-a(26) from Amiram Eldar, Mar 01 2020

STATUS

approved

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Last modified March 28 13:21 EDT 2020. Contains 333089 sequences. (Running on oeis4.)