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 A279772 #11 Dec 23 2016 21:42:16 %S A279772 2,11,20,56,65,101,110,155,200,506,515,551,560,605,650,1001,1010,1055, %T A279772 1100,1505,1550,2000,5006,5015,5051,5060,5105,5150,5501,5510,5555, %U A279772 5600,6005,6050,6500,10001,10010,10055,10100,10505,10550,11000,15005,15050,15500 %N A279772 Numbers n such that the sum of digits of 2n equals 4. %C A279772 Inspired by A088404 = A069537/2 and A279769 (the analog for 9). %t A279772 Select[Range@ 15500, Total@ IntegerDigits[2 #] == 4 &] (* _Michael De Vlieger_, Dec 23 2016 *) %o A279772 (PARI) select( is(n)=sumdigits(2*n)==4, [1..9999]) %Y A279772 Cf. A007953 (digital sum), A052216 (sumdigits(n) = 2), A279773 (sumdigits(3n) = 6), A279774 (sumdigits(4n) = 8), A279775 (sumdigits(5n) = 10), A279776 (sumdigits(6n) = 12), A279770 (sumdigits(7n) = 14), A279768 (sumdigits(8n) = 16), A279769 (sumdigits(9n) = 18), A279777 (sumdigits(9n) = 27). %Y A279772 Digital sum of m*n equals m: A088404 = A069537/2, A088405 = A052217/3, A088406 = A063997/4, A088407 = A069540/5, A088408 = A062768/6, A088409 = A063416/7, A088410 = A069543/8. %Y A279772 Cf. A005349 (Niven or Harshad numbers), A245062 (arranged in rows by digit sums). %Y A279772 Numbers with given digital sum: A011557 (1), A052216 (2), A052217 (3), A052218 (4), A052219 (5), A052220 (6), A052221 (7), A052222 (8), A052223 (9), A052224 (10), A166311 (11), A235151 (12), A143164 (13), A235225 (14), A235226 (15), A235227 (16), A166370 (17), A235228 (18), A166459 (19), A235229 (20). %K A279772 nonn,easy,base %O A279772 1,1 %A A279772 _M. F. Hasler_, Dec 23 2016