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 A382653 #21 Apr 03 2025 14:13:16
%S A382653 7,9,13,14,18,19,21,23,26,27,28,29,31,35,36,37,38,39,42,43,45,46,47,
%T A382653 49,52,53,54,56,57,58,59,61,62,63,65,67,69,70,71,72,73,74,76,77,78,79,
%U A382653 81,83,84,86,87,89,90,91,92,93,94,95,97,98,99,103,104,105,106
%N A382653 Numbers k such that a regular k-gon (k>=3) cannot be constructed with a compass, straightedge and an angle quinsector.
%H A382653 Andrew M. Gleason, <a href="http://www.jstor.org/stable/2323624">Angle Trisection, the Heptagon and the Triskaidecagon</a>, American Mathematical Monthly, 95 (1988), 185-194.
%o A382653 (Python)
%o A382653 from itertools import count, islice
%o A382653 from sympy import primefactors, totient
%o A382653 def A382653_gen(): # generator of terms
%o A382653 yield from filter(lambda n: not set(primefactors(totient(n))) <= {2,5}, count(3))
%o A382653 A382653_list = list(islice(A382653_gen(),30))
%Y A382653 Cf. A048135, A048136, A382670.
%K A382653 nonn
%O A382653 1,1
%A A382653 _Chai Wah Wu_, Apr 02 2025