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A298762 Numbers n such that uphi(n) = uphi(n+2) - uphi(n+1), where uphi is the unitary totient function (A047994). 0
1, 2, 5, 21, 9177, 244965, 14307854, 24571869, 128199057, 140830365, 401767629, 420567854, 468190437, 525970977, 780768165, 886434645, 1597167645, 4046753949, 4473784821, 5364666165, 5515718205, 11175736334, 14408460165, 18026319710, 20106993885, 20357733129 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

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

EXAMPLE

21 is in the sequence since uphi(21) = 12 = uphi(23) - uphi(22) = 22 - 10.

MATHEMATICA

uphi[n_] := If[n>1, (Times @@ (Table[ #[[1]]^ #[[2]] - 1, {1} ] & /@ FactorInteger[n]))[[1]], 1]; Select[Range[10^7], uphi[#] == uphi[# + 2] - uphi[# + 1] &]

PROG

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

isok(n) = uphi(n) == uphi(n+2) - uphi(n+1); \\ Michel Marcus, Jan 26 2018

CROSSREFS

Cf. A047994, A229552 (corresponding sequence with phi).

Sequence in context: A173313 A210575 A174143 * A025559 A072961 A249829

Adjacent sequences:  A298759 A298760 A298761 * A298763 A298764 A298765

KEYWORD

nonn

AUTHOR

Amiram Eldar, Jan 26 2018

EXTENSIONS

a(7)-a(26) from Giovanni Resta, Jan 26 2018

STATUS

approved

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Last modified September 19 16:05 EDT 2020. Contains 337178 sequences. (Running on oeis4.)