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A326889 a(1) = 1; thereafter a(n) = a(n-1) / phi(n) if phi(n) divides a(n-1), otherwise a(n) = a(n-1) * phi(n), where phi is the Euler phi-function A000010.

%I A326889 #18 Sep 21 2020 19:01:24
%S A326889 1,1,2,1,4,2,12,3,18,72,720,180,15,90,720,90,1440,240,4320,540,45,450,
%T A326889 9900,79200,3960,330,5940,495,13860,110880,3696,231,4620,73920,3080,
%U A326889 36960,1330560,73920,3080,49280,1232,14784,352,7040,168960,7680,353280,22080
%N A326889 a(1) = 1; thereafter a(n) = a(n-1) / phi(n) if phi(n) divides a(n-1), otherwise a(n) = a(n-1) * phi(n), where phi is the Euler phi-function A000010.
%C A326889 This sequence has similarities with A008336 and with A008338.
%H A326889 Rémy Sigrist, <a href="/A326889/b326889.txt">Table of n, a(n) for n = 1..2500</a>
%e A326889 The first terms, alongside phi(n), are:
%e A326889   n   a(n)  phi(n)
%e A326889   --  ----  ------
%e A326889    1     1       1
%e A326889    2     1       1
%e A326889    3     2       2
%e A326889    4     1       2
%e A326889    5     4       4
%e A326889    6     2       2
%e A326889    7    12       6
%e A326889    8     3       4
%e A326889    9    18       6
%e A326889   10    72       4
%o A326889 (PARI) for (n=1, 48, print1 (v=if (n==1, 1, v%e=eulerphi(n), v*e, v/e) ", "))
%Y A326889 See A327442 for an additive variant.
%Y A326889 Cf. A000010, A008336, A008338, A336823.
%K A326889 nonn
%O A326889 1,3
%A A326889 _Rémy Sigrist_, Sep 13 2019