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

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, 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, 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

Offset

1,3

Comments

Equals row sums of triangle A143542. - Gary W. Adamson, Aug 23 2008

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

Links

Antti Karttunen, Table of n, a(n) for n = 1..65537 (terms 1..1000 from Harry J. Smith)

Index entries for sequences computed from indices in prime factorization

Index entries for sequences related to Heinz numbers

Formula

G.f.: Sum_{k>=1} k*x^prime(k)/(1-x^prime(k)). - Vladeta Jovovic, Aug 11 2004

Additive with a(p^e) = PrimePi(p), where PrimePi(n) = A000720(n).

a(n) = A056239(A007947(n)). - Antti Karttunen, Sep 06 2018

a(n) = Sum_{p|n} A000720(p), where p is a prime. - Ridouane Oudra, Aug 19 2019

Example

a(24) = 1 + 2 = 3 because 24 = 2^3 * 3 = p(1)^3 * p(2), p(k) being the k-th prime.
From Gus Wiseman, Mar 09 2019: (Start)
The distinct prime indices of 1..20 and their sums.
   1: () = 0
   2: (1) = 1
   3: (2) = 2
   4: (1) = 1
   5: (3) = 3
   6: (1+2) = 3
   7: (4) = 4
   8: (1) = 1
   9: (2) = 2
  10: (1+3) = 4
  11: (5) = 5
  12: (1+2) = 3
  13: (6) = 6
  14: (1+4) = 5
  15: (2+3) = 5
  16: (1) = 1
  17: (7) = 7
  18: (1+2) = 3
  19: (8) = 8
  20: (1+3) = 4
(End)

Maple

with(numtheory): seq(add(pi(d), d in factorset(n)), n=1..100); # Ridouane Oudra, Aug 19 2019

Mathematica

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 *)

Prog

(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
(PARI) a(n)=my(f=factor(n)[, 1]); sum(i=1, #f, primepi(f[i])) \\ Charles R Greathouse IV, May 11 2015
(PARI) A066328(n) = vecsum(apply(primepi, (factor(n)[, 1]))); \\ Antti Karttunen, Sep 06 2018
(Python)
from sympy import primepi, primefactors
def A066328(n): return sum(map(primepi, primefactors(n))) # Chai Wah Wu, Mar 13 2024

Crossrefs

Cf. A143542. - Gary W. Adamson, Aug 23 2008

Cf. A000720, A056239, A136565.

Cf. A001221, A046660, A112798, A114638, A116861, A304360.

Sequence in context: A304740 A326619 A326567 * A373956 A330417 A330415

Adjacent sequences: A066325 A066326 A066327 * A066329 A066330 A066331

Keyword

nonn

Author

Leroy Quet, Jan 01 2002

Status

approved