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 A219340 #22 Sep 03 2025 09:15:23 %S A219340 361,551,703,1007,1273,1691,1843,2033,2071,2183,2413,2603,2641,2701, %T A219340 2831,2923,3071,3173,3293,3743,3781,4033,4313,4351,4541,5143,5263, %U A219340 5513,6023,6031,6401,6403,6623,6631,6821,7081,7141,7363,7391,7543,8303,8341,8531 %N A219340 Numbers not multiples of 9 whose digital sum coincides with digital sum of their largest proper divisor. %C A219340 Terms have a prime factor of the form 18*k+1. %H A219340 Antonio Roldán and T. D. Noe, <a href="/A219340/b219340.txt">Table of n, a(n) for n = 1..10000</a> (542 terms from Antonio Roldán) %e A219340 12673 is in the sequence because 12673 = 19*23*29, their largest proper divisor is 667. Both have a digital sum of 19. %t A219340 Select[Range[2, 10000], Mod[#, 9] > 0 && Total[IntegerDigits[#]] == Total[IntegerDigits[Divisors[#][[-2]]]] &] (* _T. D. Noe_, Nov 20 2012 *) %o A219340 (PARI) largdiv(n)=if(n==1, 1, n/factor(n)[1, 1]) \\ A032742 %o A219340 isok(n) = n>1 && sumdigits(n)==sumdigits(largdiv(n)) && n%9>0 %o A219340 select(isok, [1..10000]) /* _Antonio Roldán_, Nov 18 2012 */ %Y A219340 Cf. A032742. %K A219340 nonn,base,changed %O A219340 1,1 %A A219340 _Antonio Roldán_, Nov 18 2012