This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A109162 #25 Jul 20 2025 15:01:55 %S A109162 1,2,3,6,15,210,10659,54230826,249853434654335387610276087 %N A109162 a(1) = 1; for n > 1, a(n) = A019565(a(n-1)). %C A109162 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 A109162 Frank Adams-Watters, <a href="/A109162/b109162.txt">Table of n, a(n) for n = 1..11</a> %e A109162 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 A109162 NestList[Times @@ Prime@ Flatten@ Position[#, 1] &@ Reverse@ IntegerDigits[#, 2] &, 1, 11] (* _Michael De Vlieger_, Aug 20 2017 *) %o A109162 (Scheme, with memoization-macro definec) %o A109162 (definec (A109162 n) (if (zero? n) n (A019565 (A109162 (- n 1))))) ;; _Antti Karttunen_, Jun 18 2017 %Y A109162 Cf. A019565, A285320 (a left inverse). %Y A109162 The left edge of A285332 and A285333. %Y A109162 Cf. A153013, A328316 for similar iteration sequences, and also A376406, A376407, A376408. %K A109162 nonn %O A109162 1,2 %A A109162 _Leroy Quet_, Aug 18 2005 %E A109162 More terms from _Franklin T. Adams-Watters_, Aug 29 2006