cp's OEIS Frontend

A066328 a(n) = sum of indices of distinct prime factors of n; here, index(i-th prime) = i.

%I A066328 #43 Mar 13 2024 10:43:49
%S A066328 0,1,2,1,3,3,4,1,2,4,5,3,6,5,5,1,7,3,8,4,6,6,9,3,3,7,2,5,10,6,11,1,7,
%T A066328 8,7,3,12,9,8,4,13,7,14,6,5,10,15,3,4,4,9,7,16,3,8,5,10,11,17,6,18,12,
%U A066328 6,1,9,8,19,8,11,8,20,3,21,13,5,9,9,9,22,4,2,14,23,7,10,15,12,6,24,6,10
%N A066328 a(n) = sum of indices of distinct prime factors of n; here, index(i-th prime) = i.
%C A066328 Equals row sums of triangle A143542. - _Gary W. Adamson_, Aug 23 2008
%C A066328 a(n) = the sum of the distinct parts of the partition with Heinz number n. We define the Heinz number of a partition p = [p_1, p_2, ..., p_r] as Product_{j=1..r} (p_j-th prime) (concept used by _Alois P. Heinz_ in A215366 as an "encoding" of a partition). For example, for the partition [1, 1, 2, 4, 10] we get 2*2*3*7*29 = 2436. Example: a(75) = 5; indeed, the partition having Heinz number 75 = 3*5*5 is [2,3,3] and 2 + 3 = 5. - _Emeric Deutsch_, Jun 04 2015
%H A066328 Antti Karttunen, <a href="/A066328/b066328.txt">Table of n, a(n) for n = 1..65537</a> (terms 1..1000 from Harry J. Smith)
%H A066328 <a href="/index/Pri#prime_indices">Index entries for sequences computed from indices in prime factorization</a>
%H A066328 <a href="/index/He#Heinz">Index entries for sequences related to Heinz numbers</a>
%F A066328 G.f.: Sum_{k>=1} k*x^prime(k)/(1-x^prime(k)). - _Vladeta Jovovic_, Aug 11 2004
%F A066328 Additive with a(p^e) = PrimePi(p), where PrimePi(n) = A000720(n).
%F A066328 a(n) = A056239(A007947(n)). - _Antti Karttunen_, Sep 06 2018
%F A066328 a(n) = Sum_{p|n} A000720(p), where p is a prime. - _Ridouane Oudra_, Aug 19 2019
%e A066328 a(24) = 1 + 2 = 3 because 24 = 2^3 * 3 = p(1)^3 * p(2), p(k) being the k-th prime.
%e A066328 From _Gus Wiseman_, Mar 09 2019: (Start)
%e A066328 The distinct prime indices of 1..20 and their sums.
%e A066328    1: () = 0
%e A066328    2: (1) = 1
%e A066328    3: (2) = 2
%e A066328    4: (1) = 1
%e A066328    5: (3) = 3
%e A066328    6: (1+2) = 3
%e A066328    7: (4) = 4
%e A066328    8: (1) = 1
%e A066328    9: (2) = 2
%e A066328   10: (1+3) = 4
%e A066328   11: (5) = 5
%e A066328   12: (1+2) = 3
%e A066328   13: (6) = 6
%e A066328   14: (1+4) = 5
%e A066328   15: (2+3) = 5
%e A066328   16: (1) = 1
%e A066328   17: (7) = 7
%e A066328   18: (1+2) = 3
%e A066328   19: (8) = 8
%e A066328   20: (1+3) = 4
%e A066328 (End)
%p A066328 with(numtheory): seq(add(pi(d), d in factorset(n)), n=1..100); # _Ridouane Oudra_, Aug 19 2019
%t A066328 PrimeFactors[n_Integer] := Flatten[ Table[ #[[1]], {1}] & /@ FactorInteger[n]]; f[n_] := (Plus @@ PrimePi[ PrimeFactors[n]]); Table[ f[n], {n, 91}] (* _Robert G. Wilson v_, May 04 2004 *)
%o A066328 (PARI) { for (n=1, 1000, f=factor(n); a=0; for (i=1, matsize(f)[1], a+=primepi(f[i, 1])); write("b066328.txt", n, " ", a) ) } \\ _Harry J. Smith_, Feb 10 2010
%o A066328 (PARI) a(n)=my(f=factor(n)[,1]); sum(i=1,#f,primepi(f[i])) \\ _Charles R Greathouse IV_, May 11 2015
%o A066328 (PARI) A066328(n) = vecsum(apply(primepi,(factor(n)[,1]))); \\ _Antti Karttunen_, Sep 06 2018
%o A066328 (Python)
%o A066328 from sympy import primepi, primefactors
%o A066328 def A066328(n): return sum(map(primepi,primefactors(n))) # _Chai Wah Wu_, Mar 13 2024
%Y A066328 Cf. A143542. - _Gary W. Adamson_, Aug 23 2008
%Y A066328 Cf. A000720, A056239, A136565.
%Y A066328 Cf. A001221, A046660, A112798, A114638, A116861, A304360.
%K A066328 nonn
%O A066328 1,3
%A A066328 _Leroy Quet_, Jan 01 2002