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 A139228 #31 Oct 20 2023 08:40:37 %S A139228 22,468,7632,33542208,8556318720,128848822272,2305842870701260800, %T A139228 2658455991569831742348849607813890048, %U A139228 191561942608236104636337386514471893476304705594327040 %N A139228 First differences of perfect numbers A000396. %H A139228 Paolo Xausa, <a href="/A139228/b139228.txt">Table of n, a(n) for n = 1..14</a> %H A139228 Philippe Ellia, <a href="http://arxiv.org/abs/1210.0450">On the distance between perfect numbers</a>, arXiv:1210.0450 [math.NT], 2012. %H A139228 Florian Luca, <a href="https://www.jstor.org/stable/2589055">Problem 10711</a>, Amer. Math. Monthly, Vo. 106, No. 2 (1999) p. 166; <a href="https://www.jstor.org/stable/2695692">Can Two Consecutive Numbers Both Be Perfect?</a>, solution by Francis B. Coghlan, ibid., Vol. 108, No. 1 (2001), pp. 80-81. %H A139228 Florian Luca and Carl Pomerance, <a href="http://nyjm.albany.edu/j/2010/16-3.html">On the radical of a perfect number</a>, New York Journal of Math., Vol. 16 (2010), pp. 23-30; <a href="http://www.math.dartmouth.edu/~carlp/LucaPomeranceNYJMstyle.pdf">alternative link</a>. %H A139228 Florian Luca and Herman te Riele, <a href="http://www.nieuwarchief.nl/serie5/pdf/naw5-2011-12-1-031.pdf">phi and sigma: from Euler to Erdős</a>, Nieuw Archief voor Wiskunde, Vol. 12, No. 5 (2011), pp. 31-36. %F A139228 a(n) = A000396(n+1) - A000396(n). %F A139228 From _Amiram Eldar_, May 07 2021: (Start) %F A139228 a(n) > 1 (Luca, 1999). %F A139228 a(n) > 4 (Luca and te Riele, 2011). (End) %e A139228 a(1) = 22 because 6 and 28 are the first two perfect numbers, and their difference is 28 - 6 = 22. %t A139228 Differences[Select[Range[10000], DivisorSigma[1, #] == 2# &]] (* _Alonso del Arte_, Mar 05 2020 *) %t A139228 Differences[PerfectNumber[Range[12]]] (* _Paolo Xausa_, Oct 20 2023 *) %Y A139228 Cf. A000396, A139229, A139230, A139231, A139232, A139233, A139234, A139235, A139236, A139237. %K A139228 nonn %O A139228 1,1 %A A139228 _Omar E. Pol_, Apr 18 2008 %E A139228 More terms from _Omar E. Pol_, Oct 02 2012