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 A359839 #13 Jan 05 2025 19:51:42
%S A359839 2023,4912,12103,17575,23273,51424,52675,60399,78650,80800,87723,
%T A359839 93624,100303,112624,117962,121224,122875,182182,193075,200752,228175,
%U A359839 235024,245725,245726,249500,263275,306963,320704,333475,373490,403675,416583,421072,444624,448000
%N A359839 Numbers k such that k, k + 1 and k + 2 are 3 consecutive Niven (Harshad) numbers that are also divisible by a square.
%C A359839 Equivalently, smallest of 3 consecutive numbers each divisible by a square and also divisible by the sum of their digits (Niven numbers).
%D A359839 Jean-Marie De Koninck, Ces nombres qui nous fascinent, Entry 48, p. 18, Ellipses, Paris, 2008.
%D A359839 Jean-Marie De Koninck, Those Fascinating Numbers, Entry 110, p. 36, American Mathematical Society, 2009.
%H A359839 Curtis Cooper and Robert E. Kennedy, <a href="https://web.archive.org/web/2024*/https://www.fq.math.ca/Scanned/31-2/cooper.pdf">On consecutive Niven numbers</a>, Fibonacci Quarterly, Vol. 21, No. 2 (1993), pp. 146-151.
%H A359839 Giovanni Resta, <a href="https://www.numbersaplenty.com/set/Harshad_number/">Harshad numbers</a>.
%H A359839 Wikipedia, <a href="http://en.wikipedia.org/wiki/Harshad_number">Harshad number</a>.
%e A359839 2023 = 7 * 17^2 = 289 * (2+0+2+3); 2024 = 506 * 2^2 = 253 * (2+0+2+4) and 2025 = 81 * 5^2 = 225 * (2+0+2+5) hence 2023 is a term.
%t A359839 q[n_] := Divisible[n, Total@IntegerDigits[n]] && ! SquareFreeQ[n]; tri = q /@ Range[3]; seq = {}; Do[tri = Join[Rest[tri], {q[k]}]; If[And @@ tri, AppendTo[seq, k - 2]], {k, 3, 5*10^5}]; seq (* _Amiram Eldar_, Jan 15 2023 *)
%Y A359839 Intersection of A070258 and A154701.
%Y A359839 Cf. A013929, A068781, A235578.
%Y A359839 Cf. A005349, A060159, A141769, A330927, A330928, A330929, A330930.
%K A359839 nonn,base
%O A359839 1,1
%A A359839 _Bernard Schott_, Jan 15 2023
%E A359839 More terms from _Amiram Eldar_, Jan 15 2023