cp's OEIS Frontend

A076387 Numbers n such that sum of digits in base 9 is a divisor of sum of prime divisors (A008472).

%I A076387 #33 Sep 08 2022 08:45:07
%S A076387 2,3,5,7,9,21,27,65,69,70,81,84,90,110,123,126,130,133,154,189,222,
%T A076387 228,243,252,259,264,327,329,333,340,342,343,350,365,372,381,402,434,
%U A076387 450,516,528,580,588,618,621,650,684,729,730,731,738,740,741,756,765,774
%N A076387 Numbers n such that sum of digits in base 9 is a divisor of sum of prime divisors (A008472).
%C A076387 The sequence is infinite because, for m = 9^k, k >= 0, digsum(m_9) = 1. - _Marius A. Burtea_, Jul 10 2019
%H A076387 Marius A. Burtea, <a href="/A076387/b076387.txt">Table of n, a(n) for n = 1..5189</a>
%e A076387 21 = 23_9, digsum(23_9) = 5, PrimeDivisors(21) = {3, 7}, sopf(21) = 3+7 = 10 = 5*2.
%p A076387 A076387 := proc(n) local i,j,t,t1, sod, sopd; t := NULL; for i from 2 to n do t1 := i; sod := 0; while t1 <> 0 do sod := sod + (t1 mod 9); t1 := floor(t1/9); od; sopd := 0; j := 1; while ithprime(j) <= i do if i mod ithprime(j) = 0 then sopd := sopd+ithprime(j); fi; j := j+1; od; if sopd mod sod = 0 then t := t,i; fi; od; t; end;
%o A076387 (PARI) {for(ixp=2,783,
%o A076387 casi=ixp;cvst=0;dsu=0;M=factor(ixp);smt=0;
%o A076387 for(i=1,matsize(M)[1],smt=smt+M[i, 1]);
%o A076387 while(casi!=0,
%o A076387 cvd=casi%9;dsu=dsu+cvd;casi=(casi-cvd)/9);
%o A076387 if(smt%dsu==0,print1(ixp,", ")))} \\ _Douglas Latimer_, May 08 2012
%o A076387 (Magma) [n: n in [1..800]| &+PrimeDivisors(n) mod &+Intseq(n,9) eq 0] ; // _Marius A. Burtea_, Jul 10 2019
%Y A076387 Cf. A075657, A076380 - A076387.
%K A076387 nonn,base
%O A076387 1,1
%A A076387 _Floor van Lamoen_, Oct 08 2002