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 A008555 #20 Jul 08 2025 01:05:12
%S A008555 1,2,5,6,29,7,169,34,197,41,5741,33,33461,239,1345,1154,1136689,199,
%T A008555 6625109,1121,45697,8119,225058681,1153,45232349,47321,7761797,38081,
%U A008555 44560482149,961,259717522849,1331714,52734529,1607521,1800193921,39201
%N A008555 Primitive parts of Pell numbers.
%C A008555 Also called Sylvester-Pell cyclotomic numbers. - _Paul Barry_, Apr 15 2005
%C A008555 According to Guy, Raphael Robinson noticed that a(7) and a(30) are squares and asked if there are more. There are no others in the first 10000 terms. [_T. D. Noe_, May 07 2009]
%D A008555 R. K. Guy, Unsolved Problems in Number Theory, A3.
%H A008555 T. D. Noe, <a href="/A008555/b008555.txt">Table of n, a(n) for n=1..1000</a>
%H A008555 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/SylvesterCyclotomicNumber.html">Sylvester Cyclotomic Number</a>. - _Paul Barry_, Apr 15 2005
%F A008555 a(n) = A000129(n) / Product_{d<n,d|n} a(d). [_T. D. Noe_, May 07 2009]
%F A008555 a(n) = Product_{k=1..n-1} if(gcd(n, k)=1, (1+sqrt(2))-(1-sqrt(2))*exp(2*Pi*I*k/n), 1), I=sqrt(-1). - _Paul Barry_, Apr 15 2005
%e A008555 a(8)=34 because pell(8)=408 and 408/(a(4)*a(2)*a(1)) = 408/12 = 34. [From _T. D. Noe_, May 07 2009]
%t A008555 pell={1,2}; pp={1,2}; Do[s=2*pell[[ -1]]+pell[[ -2]]; AppendTo[pell,s]; AppendTo[pp, s/Times@@pp[[Most[Divisors[n]]]]], {n,3,40}]; pp (* _T. D. Noe_, May 07 2009 *)
%Y A008555 Cf. A061446 (primitive part of Fibonacci numbers). [_T. D. Noe_, May 07 2009]
%Y A008555 Cf. A105606.
%K A008555 nonn
%O A008555 1,2
%A A008555 _N. J. A. Sloane_
%E A008555 Corrected and extended by _T. D. Noe_, May 07 2009
%E A008555 Edited by _N. J. A. Sloane_, Oct 04 2009