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A332973 Solutions k of the equation usigma(k) = usigma(k-1) + usigma(k-2) where usigma(k) is the sum of unitary divisors of k (A034448).

%I A332973 #11 Mar 10 2020 21:56:38
%S A332973 3,42,188970,998670,51670374,91397154,236280786,259172826,792554574,
%T A332973 1106710914,1468869930,1957827498,2467823442,2496238590,3324585210,
%U A332973 4055970282,4183629690,4384566870,13479861630,20681058270,29343074178,43449285210,68705958690,71418085926
%N A332973 Solutions k of the equation usigma(k) = usigma(k-1) + usigma(k-2) where usigma(k) is the sum of unitary divisors of k (A034448).
%H A332973 Giovanni Resta, <a href="/A332973/b332973.txt">Table of n, a(n) for n = 1..64</a> (terms < 10^13)
%e A332973 42 is a term since s(42) = 96 and s(40) + s(41) = 54 + 42 = 96.
%t A332973 usigma[1] = 1; usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); Select[Range[3, 10^8], usigma[#] == usigma[# - 1] + usigma[# - 2] &]
%o A332973 (PARI) usigma(k) = sumdivmult(k, d, if(gcd(d, k/d)==1, d)); \\ A034448
%o A332973 isok(k) = usigma(k) == usigma(k-1) + usigma(k-2); \\ _Jinyuan Wang_, Mar 08 2020
%Y A332973 The unitary version of A065900.
%Y A332973 Cf. A034448, A065557, A075565, A076136, A145469, A291126, A291176, A292033, A294995, A332974.
%K A332973 nonn
%O A332973 1,1
%A A332973 _Amiram Eldar_, Mar 04 2020
%E A332973 Terms a(22) and beyond from _Giovanni Resta_, Mar 10 2020