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 A140173 #24 Jul 07 2025 15:42:43 %S A140173 1,6,3720,25080,237000,353430,1201560,1402440,2104440,2147040,4140360, %T A140173 22007160,60035220,104370420,110095020,136222020,402500280,2203551000, %U A140173 2223003120,8720021310,35590401000,110232105060,116046010080,212062116000,440401221000,2181301242120 %N A140173 Numbers k such that sigma(k) = phi(k)*(sum of the digits of k). %C A140173 Is it true that 10 divides all multi-digit terms of the sequence? %H A140173 Amiram Eldar, <a href="/A140173/b140173.txt">Table of n, a(n) for n = 1..36</a> (calculated using data from _Jud McCranie_) %e A140173 sigma(237000) = phi(237000)*(2+3+7+0+0+0). %t A140173 Select[Range[10^6],DivisorSigma[1,#]==EulerPhi[#]*DigitSum[#]&] (* _James C. McMahon_, Jul 06 2025 *) %Y A140173 Subsequence of A020492. %Y A140173 Cf. A140174. %K A140173 base,nonn %O A140173 1,2 %A A140173 _Farideh Firoozbakht_, May 15 2008 %E A140173 a(13)-a(19) from _Sean A. Irvine_, Sep 23 2009 %E A140173 a(20)-a(25) from _Donovan Johnson_, Mar 06 2012 %E A140173 a(26) from _Amiram Eldar_, Dec 04 2019, using data from _Jud McCranie_