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 A230458 #52 May 26 2019 15:17:04
%S A230458 9,1,9,2,6,3,1,7,7,0
%N A230458 Decimal expansion of Δν_{Cs} in unit s^{-1}; one of the seven units of the 2019 SI system.
%C A230458 The second s is defined to be exactly 9192631770 periods of the resonance frequency of the hyperfine transition of the cesium 133 atom.
%C A230458 Prime factors of this number are 2^1, 3^2, 5^1, 7^2, 47^1, 44351^1. - _John W. Nicholson_, Jun 15 2014
%C A230458 The value was fixed in 1968 by the 13th CGPM in terms of periods of the radiation due to the transition between the two hyperfine levels of the ground state of 133Cs atoms. - _Stanislav Sykora_, Mar 30 2015
%C A230458 In the 2019 SI system of units (see the BIPM link, and A322415) one of the seven units is Δν_{Cs} = Δν(^{133}Cs)_{hfs} = 9192631770 s^{-1}. - _Wolfdieter Lang_, Feb 12 2019
%H A230458 BIPM, <a href="https://www.bipm.org/utils/common/pdf/CGPM-2018/26th-CGPM-Resolutions.pdf">On the revision of the International System of Units (SI)</a>, BIPM, Nov 13-16 2018.
%H A230458 Bureau International des Poids et Mesures, <a href="http://www.bipm.org/en/publications/si-brochure/second.html">Unit of time (second)</a>
%H A230458 W. M. Itano and N. F. Ramsey, <a href="http://www.scientificamerican.com/article/accurate-measurement-of-time/">Accurate measurement of time</a>, Scientific American, 269 (July 1993), 56-65.
%H A230458 N. F. Ramsey, <a href="http://www.jstor.org/stable/27854962">Precise measurement of time</a>, American Scientist, 76 (No. 1, 1988), 42-49.
%H A230458 Wikipedia, <a href="http://en.wikipedia.org/wiki/Second">Second</a>
%H A230458 Wikipedia, <a href="https://en.wikipedia.org/wiki/2019_redefinition_of_SI_base_units">2019 redefinition of SI base units</a>
%F A230458 Δν_{Cs} = 9192631770 s^{-1}.
%e A230458 c = 9192631770 m/s.
%t A230458 IntegerDigits@ 9192631770 (* _Michael De Vlieger_, Mar 30 2015 *)
%Y A230458 Cf. A003678 (c), A003676 (h), A081823 (e), A070063 (k), A322578 (N_A), A244823, A322415.
%K A230458 nonn,cons,fini,full
%O A230458 10,1
%A A230458 _N. J. A. Sloane_, Oct 19 2013