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A176707 Sum of digits of all distinct prime factors of n-th semiprime.

%I A176707 #10 Feb 06 2021 00:05:44
%S A176707 2,5,3,7,9,8,10,4,5,6,5,10,12,12,7,7,7,11,7,13,13,6,9,8,12,9,7,13,9,
%T A176707 14,11,7,13,15,10,13,10,16,15,2,9,8,10,17,15,14,10,6,16,12,9,18,11,12,
%U A176707 13,4,17,19,10,15,10,18,16,4,18,10,6,12,11,10,12,11,12,13,12,7,16,19,14,14,7
%N A176707 Sum of digits of all distinct prime factors of n-th semiprime.
%H A176707 Michael S. Branicky, <a href="/A176707/b176707.txt">Table of n, a(n) for n = 1..10000</a>
%e A176707 a(1)=2 because 1st semiprime=2*2 and 2=2; a(2)=5 because 2nd semiprime=2*3 and 2<3.
%p A176707 A007953 := proc(n) add(d,d=convert(n,base,10)) ; end proc:
%p A176707 A176707 := proc(n) s := A001358(n) ; add( A007953(p), p = numtheory[factorset](s) ) ; end proc: seq(A176707(n),n=1..120) ; # _R. J. Mathar_, Apr 25 2010
%o A176707 (Python)
%o A176707 from sympy import factorint
%o A176707 def aupton(terms):
%o A176707   alst, m = [], 4
%o A176707   while len(alst) < terms:
%o A176707     f = factorint(m)
%o A176707     if sum(f.values()) == 2: # semiprime
%o A176707       alst.append(sum(sum(map(int, str(p))) for p in f.keys()))
%o A176707     m += 1
%o A176707   return alst
%o A176707 print(aupton(81)) # _Michael S. Branicky_, Feb 05 2021
%Y A176707 Cf. A095402.
%K A176707 nonn,base
%O A176707 1,1
%A A176707 _Juri-Stepan Gerasimov_, Apr 24 2010
%E A176707 a(13), a(34) etc. corrected by - _R. J. Mathar_, Apr 25 2010