A140645 - OEIS

%I #18 May 16 2026 16:50:03

%S 1,2,4,6,3,6,9,12,6,3,9,6,9,9,12,9,15,9,9,18,9,9,9,9,18,18,9,18,18,18,

%T 18,18,18,18,36,18,27,18,18,18,18

%N Digit sums of highly composite numbers.

%C Except for the first three terms, all others are multiples of 3.

%H Amiram Eldar, <a href="/A140645/b140645.txt">Table of n, a(n) for n = 1..10000</a>

%H Achim Flammenkamp, <a href="https://wwwhomes.uni-bielefeld.de/achim/HCN/highly.txt">Table of 1200 Highly Composite Numbers</a>.

%H Graeme McRae, <a href="https://web.archive.org/web/20190223125015/http://2000clicks.com/mathhelp/NumberFactorsHighlyComposite.aspx">Highly Composite Numbers</a>.

%F a(n) = A007953(A002182(n)). - _Amiram Eldar_, Nov 13 2019

%e 2162160 is a highly composite number whose digit sum is 18.

%t HCN=NestList[Function[last,Module[{d = DivisorSigma[0, last]},NestWhile[# + 1 &, last, DivisorSigma[0, #] <= d &]]], 1,40]; DigitSum/@HCN (* _James C. McMahon_, Jul 12 2025 *)

%Y Cf. A002182, A002183, A007953, A117825, A127390.

%K nonn,base

%O 1,2

%A _Parthasarathy Nambi_, Jul 08 2008