A268387 - OEIS

A268387

Bitwise-XOR of the exponents of primes in the prime factorization of n.

0, 1, 1, 2, 1, 0, 1, 3, 2, 0, 1, 3, 1, 0, 0, 4, 1, 3, 1, 3, 0, 0, 1, 2, 2, 0, 3, 3, 1, 1, 1, 5, 0, 0, 0, 0, 1, 0, 0, 2, 1, 1, 1, 3, 3, 0, 1, 5, 2, 3, 0, 3, 1, 2, 0, 2, 0, 0, 1, 2, 1, 0, 3, 6, 0, 1, 1, 3, 0, 1, 1, 1, 1, 0, 3, 3, 0, 1, 1, 5, 4, 0, 1, 2, 0, 0, 0, 2, 1, 2, 0, 3, 0, 0, 0, 4, 1, 3, 3, 0, 1, 1, 1, 2, 1, 0, 1, 1, 1, 1, 0, 5, 1, 1, 0, 3, 3, 0, 0, 3

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,4

COMMENTS

The sums of the first 10^k terms, for k = 1, 2, ..., are 11, 139, 1427, 14207, 141970, 1418563, 14183505, 141834204, 1418330298, 14183245181, ... . Apparently, the asymptotic mean of this sequence is limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = 1.4183... . - Amiram Eldar, Sep 10 2022

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10000

Index entries for sequences computed from exponents in factorization of n.

FORMULA

a(1) = 0; for n > 1: a(n) = A067029(n) XOR a(A028234(n)). [Here XOR stands for bitwise exclusive-or, A003987.]

Other identities and observations. For all n >= 1:

a(n) <= A267116(n) <= A001222(n).

From Peter Munn, Dec 02 2019 with XOR used as above: (Start)

Defined by: a(p^k) = k, for prime p; a(A059897(n,k)) = a(n) XOR a(k).

a(A052330(n XOR k)) = a(A052330(n)) XOR a(A052330(k)).

a(A019565(n XOR k)) = a(A019565(n)) XOR a(A019565(k)).

(End)

MATHEMATICA

Table[BitXor @@ Map[Last, FactorInteger@ n], {n, 120}] (* Michael De Vlieger, Feb 12 2016 *)

PROG

(Scheme, with memoization-macro definec)

(definec (A268387 n) (cond ((= 1 n) 0) (else (A003987bi (A067029 n) (A268387 (A028234 n)))))) ;; A003987bi implements bitwise-xor (see A003987).

(PARI) a(n) = {my(f = factor(n)); my(b = 0); for (k=1, #f~, b = bitxor(b, f[k, 2]); ); b; } \\ Michel Marcus, Feb 06 2016

(Python)

from functools import reduce

from operator import xor

from sympy import factorint

def A268387(n): return reduce(xor, factorint(n).values(), 0) # Chai Wah Wu, Aug 31 2022

CROSSREFS

A003987, A028234, A059897 and A067029 are used to express relationships between sequence terms.

Cf. A268390 (indices of zeros).

Sequences with similar definitions: A267115, A267116.

Differs from A136566 for the first time at n=24, where a(24) = 2, while A136566(24) = 4.

Cf. A019565, A052330.

Sequence in context: A319273 A329615 A272894 * A136566 A330235 A048983

Adjacent sequences: A268384 A268385 A268386 * A268388 A268389 A268390

KEYWORD

nonn,base

AUTHOR

Antti Karttunen, Feb 05 2016

STATUS

approved