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a(1) = 1; for n > 1, a(n) = A019565(a(n-1)).
5

%I #21 Aug 20 2017 23:30:44

%S 1,2,3,6,15,210,10659,54230826,249853434654335387610276087

%N a(1) = 1; for n > 1, a(n) = A019565(a(n-1)).

%C After the initial 1, even-indexed terms are of the form 4k+2 (members of A016825) and odd-indexed terms are of the form 6k+3 (members of A016945). However, not all even terms after 2 are multiples of three, because not all odd-indexed terms are of the form 4k+3. For example, because a(11) is of the form 4k+1, a(12) cannot be a multiple of three. - _Antti Karttunen_, Jun 18 2017

%H Frank Adams-Watters, <a href="/A109162/b109162.txt">Table of n, a(n) for n = 1..11</a>

%e a(4) = 6, which is 110 in binary. So a(5) is the product of the primes corresponding to the 1's of 110, 3*5 = 15.

%t NestList[Times @@ Prime@ Flatten@ Position[#, 1] &@ Reverse@ IntegerDigits[#, 2] &, 1, 11] (* _Michael De Vlieger_, Aug 20 2017 *)

%o (Scheme, with memoization-macro definec)

%o (definec (A109162 n) (if (zero? n) n (A019565 (A109162 (- n 1))))) ;; _Antti Karttunen_, Jun 18 2017

%Y Cf. A019565, A285320 (a left inverse).

%Y The left edge of A285332 and A285333.

%K nonn

%O 1,2

%A _Leroy Quet_, Aug 18 2005

%E More terms from _Franklin T. Adams-Watters_, Aug 29 2006