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 A366779 #24 Feb 05 2024 18:23:55 %S A366779 1,1,1,1,1,1,1,1,1,1,2,1,1,1,1,1,2,1,2,1,1,2,4,1,2,1,2,1,2,1,2,1,2,2, %T A366779 1,1,2,2,1,1,2,1,2,2,1,4,10,1,2,2,2,1,2,2,2,1,2,2,6,1,2,2,1,2,1,2,4,2, %U A366779 4,1,2,1,2,2,2,2,2,1,2,1,6,2,4,1,2,2,2 %N A366779 a(n) = lambda(lambda(lambda(n))), where lambda(n) is the Carmichael lambda function (A002322). %H A366779 Alois P. Heinz, <a href="/A366779/b366779.txt">Table of n, a(n) for n = 1..20000</a> %H A366779 N. Harland, <a href="https://arxiv.org/abs/1111.3667">The iterated Carmichael lambda function</a>, arXiv:1111.3667 [math.NT], 2011. %H A366779 G. Martin and C. Pomerance, <a href="http://www.math.dartmouth.edu/~carlp/PDF/lambda030205.pdf">The iterated Carmichael lambda-function and the number of cycles of the power generator</a>, Acta Arith. 118:4 (2005), pp. 305-335. %F A366779 a(n) = A002322(A181776(n)). %e A366779 a(5) = 1, since A181776(5) = 2, and A002322(2) = 1. %p A366779 a:= n-> (numtheory[lambda]@@3)(n): %p A366779 seq(a(n), n=1..100); # _Alois P. Heinz_, Jan 19 2024 %t A366779 a[n_]:=Nest[CarmichaelLambda,n,3]; Array[a,87] (* _Stefano Spezia_, Jan 20 2024 *) %o A366779 (PARI) a(n) = lcm(znstar(lcm(znstar(lcm(znstar(11)[2]))[2]))[2]) %o A366779 (Python) %o A366779 from sympy import reduced_totient %o A366779 def A366779(n): return reduced_totient(reduced_totient(reduced_totient(n))) # _Chai Wah Wu_, Jan 29 2024 %Y A366779 Cf. A002322 (lambda function), A181776 (lambda function at two iterations). %K A366779 nonn %O A366779 1,11 %A A366779 _Miles Englezou_, Dec 15 2023