A101080 -id:A101080 - cp's OEIS frontend

A261075 Semiprimes whose prime factors are of equal binary length and which differ from each other in exactly three bit positions.

527, 551, 1591, 2173, 2491, 2623, 3127, 5183, 5963, 6059, 6557, 6767, 6887, 7031, 7373, 7571, 7597, 7739, 7979, 8051, 8249, 8549, 8633, 8881, 9017, 9523, 9701, 10541, 10807, 11303, 11639, 12091, 12317, 12827, 14351, 19519, 20413, 20989, 21823, 22331, 23213, 24047, 24613, 24881, 24883, 25777, 25807, 26549, 26671, 26827, 26989, 27661, 28199, 28459, 28757, 29329

Offset: 1

Antti Karttunen, Sep 22 2015

			291311 = 523 * 557 is included (as term a(334)) because 523 ("1000001011" in binary) and 557 ("1000101101" in binary) differ in exactly three bit-positions.

Antti Karttunen, Table of n, a(n) for n = 1..10000
N. S. Dattani & N. Bryans, Quantum factorization of 56153 with only 4 qubits, arXiv:1411.6758 [quant-ph], 2014.

Cf. A000523, A001222, A006530, A020639, A101080.
Cf. also A261073, A261074.
Subsequence of A085721.

Select[Range@ 30000, And[Length@ # == 2, IntegerLength[#1, 2] == IntegerLength[#2, 2] & @@ #, Total@ BitXor[IntegerDigits[#1, 2], IntegerDigits[#2, 2]] == 3 & @@ #] &@ Flatten@ Map[ConstantArray[#1, #2] & @@ # &, FactorInteger@ #] &] (* Michael De Vlieger, Oct 08 2016 *)

A000523 = n -> logint(n, 2);
A020639(n) = if(1==n,n,vecmin(factor(n)[, 1]));
isA261075(n) = { my(a,b); if(bigomega(n)!=2, 0, a = A020639(n); b = (n/a); ((A000523(a) == A000523(b)) && (3 == norml2(binary(bitxor(a,b)))))); };
i=0; n=0; while(i < 10000, n++; if(isA261075(n), i++; write("b261075.txt", i, " ", n)));

;; With Antti Karttunen's IntSeq-library.
(define A261075 (MATCHING-POS 1 1 (lambda (n) (and (= 2 (A001222 n)) (= (A000523 (A020639 n)) (A000523 (A006530 n))) (= 3 (A101080bi (A020639 n) (A006530 n)))))))

A261077 Semiprimes whose prime factors differ from each other in one bit position only.

Original entry on oeis.org

6, 21, 33, 35, 57, 65, 161, 185, 201, 323, 377, 393, 437, 473, 497, 713, 899, 1529, 1577, 1763, 1769, 1841, 1961, 2021, 2537, 3233, 3473, 3497, 3737, 4553, 4601, 4757, 5561, 5609, 5753, 6497, 7217, 7313, 9593, 9797, 10265, 10403, 10841, 10961, 11009, 12297, 14129, 15689, 17513, 18209, 19043, 19337, 21353, 22499, 23129, 23393, 26969, 27221, 27233, 29177

Offset: 1

Antti Karttunen, Sep 22 2015

			21 = 3*7 is present because 3 in binary is "11" ("011" when extended with a leading zero) and 7 in binary is "111", and these differ only in the bit-position 2 (with indexing where the least significant bit is in the position 0).
33 = 3*11 is present because 3 in binary is "11" ("0011" when extended with two leading zeros) and 11 in binary is "1011", and these differ only in the bit-position 3.

Antti Karttunen, Table of n, a(n) for n = 1..5000

Cf. A000523, A001222, A006530, A020639, A101080.
Cf. also A261073, A261080 (subsequences).
Subsequence of A261078.
Gives the positions of ones in A260737.

A020639(n) = if(1==n,n,vecmin(factor(n)[, 1]));
isA261077 = n -> if(bigomega(n)!=2, 0, (1 == norml2(binary(bitxor((n/A020639(n)),A020639(n))))));
i=0; n=0; while(i < 5000, n++; if(isA261077(n), i++; write("b261077.txt", i, " ", n)));

;; With Antti Karttunen's IntSeq-library.
(define A261077 (MATCHING-POS 1 1 (lambda (n) (and (= 2 (A001222 n)) (= 1 (A101080bi (A020639 n) (A006530 n)))))))

A260737 Sum of Hamming distances between binary representations of prime factors of n, summed over all nonordered pairs of primes present (with multiplicity) in the prime factorization of n.

Original entry on oeis.org

0, 0, 0, 0, 0, 1, 0, 0, 0, 3, 0, 2, 0, 2, 2, 0, 0, 2, 0, 6, 1, 2, 0, 3, 0, 4, 0, 4, 0, 6, 0, 0, 1, 3, 1, 4, 0, 2, 3, 9, 0, 4, 0, 4, 4, 3, 0, 4, 0, 6, 2, 8, 0, 3, 3, 6, 1, 5, 0, 10, 0, 4, 2, 0, 1, 4, 0, 6, 2, 6, 0, 6, 0, 4, 4, 4, 2, 8, 0, 12, 0, 4, 0, 7, 2, 3, 4, 6, 0, 9, 2, 6, 3, 4, 3, 5, 0, 4, 2, 12, 0, 6, 0, 12, 4, 5, 0, 6, 0, 8, 3, 8, 0, 4, 2, 10, 6, 4, 3, 14

Offset: 1

Antti Karttunen, Sep 22 2015

			For n = 1 the prime factorization is empty, thus there is nothing to sum, so a(1) = 0.
For n = 6 = 2*3, a(6) = 1 because the Hamming distance between 2 and 3 is 1 as 2 = "10" in binary and 3 = "11" in binary.
For n = 10 = 2*5, a(10) = 3 because the Hamming distance between 2 and 5 is 3 as 2 = "10" in binary (extended with a leading zero to make it "010") and 5 = "101" in binary.
For n = 12 = 2*2*3, a(12) = 2 because the Hamming distance between 2 and 3 is 1, and the pair (2,3) occurs twice as one can pick either one of the two 2's present in the prime factorization to be a pair of a single 3. Note that the Hamming distance between 2 and 2 is 0, thus the pair (2,2) of prime divisors does not contribute to the sum.
For n = 36 = 2*2*3*3, a(36) = 4 because the Hamming distance between 2 and 3 is 1, and the prime factor pair (2,3) occurs four times in total. Note that the Hamming distance is zero between 2 and 2 as well as between 3 and 3, thus the pairs (2,2) and (3,3) do not contribute to the sum.

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

Cf. A101080.
Cf. A000961 (positions of the zeros), A261077 (positions of the ones).
Cf. A072594, A072595, A235488.
Cf. also A261079.

A268726 Index of the toggled bit between n and A268717(n+1): a(n) = A000523(A003987(n, A268717(1+n))).

Original entry on oeis.org

0, 1, 2, 0, 3, 0, 0, 1, 4, 0, 0, 1, 0, 1, 2, 0, 5, 0, 0, 1, 0, 1, 2, 0, 0, 1, 2, 0, 3, 0, 0, 1, 6, 0, 0, 1, 0, 1, 2, 0, 0, 1, 2, 0, 3, 0, 0, 1, 0, 1, 2, 0, 3, 0, 0, 1, 4, 0, 0, 1, 0, 1, 2, 0, 7, 0, 0, 1, 0, 1, 2, 0, 0, 1, 2, 0, 3, 0, 0, 1, 0, 1, 2, 0, 3, 0, 0, 1, 4, 0, 0, 1, 0, 1, 2, 0, 0, 1, 2, 0, 3, 0, 0, 1, 4, 0, 0, 1, 0, 1, 2, 0, 5, 0, 0, 1, 0, 1, 2, 0, 0

Offset: 0

Antti Karttunen, Feb 13 2016

A fractal sequence, because a permutation of A007814. Removing zeros yields A268727(n) = a(n)+1.

Antti Karttunen, Table of n, a(n) for n = 0..16383
Indranil Ghosh, C program to generate the sequence

One less than A268727.
Cf. A003188, A006068.
Cf. A000523, A003987, A007814, A101080, A268717.
Cf. also array A268833.

A003188[n_]:=BitXor[n, Floor[n/2]]; A006068[n_]:=If[n<2, n, Block[{m=A006068[Floor[n/2]]}, 2m + Mod[Mod[n,2] + Mod[m, 2], 2]]]; A268717[n_]:=If[n<1, 0, A003188[1 + A006068[n - 1]]]; a[n_]:= Floor[Log[2, BitXor[n, A268717[n + 1]]]]; Table[a[n], {n, 0, 200}] (* Indranil Ghosh, Apr 02 2017 *)

A003188(n) = bitxor(n, n\2);
A006068(n) = if(n<2, n, {my(m = A006068(n\2)); 2*m + (n%2 + m%2)%2});
A268717(n) = if(n<1, 0, A003188(1 + A006068(n - 1)));
for(n=0, 200, print1(logint(bitxor(n, A268717(n + 1)), 2),", "))  \\ Indranil Ghosh, Apr 02 2017

def A003188(n): return n^(n//2)
def A006068(n):
    if n<2: return n
    else:
        m=A006068(n//2)
        return 2*m + (n%2 + m%2)%2
def A268717(n): return 0 if n<1 else A003188(1 + A006068(n - 1))
print([int(math.floor(math.log(n^A268717(n + 1), 2))) for n in range(201)]) # Indranil Ghosh, Apr 02 2017

(define (A268726 n) (A000523 (A003987bi n (A268717 (+ 1 n))))) ;; A003987bi implements the bitwise-XOR, defined in A003987.

a(n) = A007814(1 + A006068(n)).
a(n) = A000523(A003987(n, A268717(1+n))).
a(n) = floor(log_2(n XOR A003188(1 + A006068(n)))).
Other identities:
For all n >= 1, a(A003188(n-1)) = A007814(n).

A268727 One-based index of the toggled bit between n and A268717(n+1): a(n) = A070939(A003987(n,A268717(1+n))).

Original entry on oeis.org

1, 2, 3, 1, 4, 1, 1, 2, 5, 1, 1, 2, 1, 2, 3, 1, 6, 1, 1, 2, 1, 2, 3, 1, 1, 2, 3, 1, 4, 1, 1, 2, 7, 1, 1, 2, 1, 2, 3, 1, 1, 2, 3, 1, 4, 1, 1, 2, 1, 2, 3, 1, 4, 1, 1, 2, 5, 1, 1, 2, 1, 2, 3, 1, 8, 1, 1, 2, 1, 2, 3, 1, 1, 2, 3, 1, 4, 1, 1, 2, 1, 2, 3, 1, 4, 1, 1, 2, 5, 1, 1, 2, 1, 2, 3, 1, 1, 2, 3, 1, 4, 1, 1, 2, 5, 1, 1, 2, 1, 2, 3, 1, 6, 1, 1, 2, 1, 2, 3, 1, 1

Offset: 0

Antti Karttunen, Feb 13 2016

A fractal sequence like A268726.

Antti Karttunen, Table of n, a(n) for n = 0..8191

One more than A268726.
Cf. A003188, A006068.
Cf. A001511, A003987, A010059, A070939, A101080, A268717.
Cf. also array A268833.

(define (A268727 n) (A070939 (A003987bi n (A268717 (+ 1 n)))))  ;; A003987bi implements the bitwise-XOR, defined in A003987.

a(n) = A001511(1+A006068(n)).
a(n) = A070939(A003987(n,A268717(1+n))).
a(n) = 1 + floor(log_2(n XOR A003188(1+A006068(n)))).
a(n) = A001511(n)*(1-A010059(n)) + 1. - Alan Michael Gómez Calderón, Jun 15 2025

A268834 Transpose of array A268833.

Original entry on oeis.org

0, 1, 0, 2, 1, 0, 1, 2, 1, 0, 2, 3, 2, 1, 0, 3, 2, 3, 2, 1, 0, 2, 1, 2, 1, 2, 1, 0, 1, 2, 3, 2, 3, 2, 1, 0, 2, 3, 4, 3, 2, 1, 2, 1, 0, 3, 2, 3, 4, 3, 2, 1, 2, 1, 0, 4, 3, 2, 3, 4, 3, 2, 3, 2, 1, 0, 3, 4, 1, 2, 3, 4, 3, 2, 3, 2, 1, 0, 2, 3, 2, 3, 2, 3, 2, 1, 2, 1, 2, 1, 0, 3, 2, 3, 2, 3, 2, 1, 2, 3, 2, 1, 2, 1, 0, 2, 1, 2, 1, 4, 3, 2, 3, 4, 3, 2, 3, 2, 1, 0

Offset: 0

Antti Karttunen, Feb 15 2016

See comments in A268833.

			The top left [0 .. 16] x [0 .. 16] section of the array:
  0, 1, 2, 1, 2, 3, 2, 1, 2, 3, 4, 3, 2, 3, 2, 1, 2
  0, 1, 2, 3, 2, 1, 2, 3, 2, 3, 4, 3, 2, 1, 2, 3, 2
  0, 1, 2, 3, 2, 3, 4, 3, 2, 1, 2, 3, 2, 3, 4, 3, 2
  0, 1, 2, 1, 2, 3, 4, 3, 2, 3, 2, 1, 2, 3, 4, 3, 2
  0, 1, 2, 3, 2, 3, 4, 3, 2, 3, 4, 5, 4, 3, 4, 3, 2
  0, 1, 2, 1, 2, 3, 4, 3, 2, 3, 4, 3, 4, 5, 4, 3, 2
  0, 1, 2, 1, 2, 3, 2, 1, 2, 3, 4, 3, 4, 5, 4, 3, 2
  0, 1, 2, 3, 2, 1, 2, 3, 2, 3, 4, 5, 4, 3, 4, 3, 2
  0, 1, 2, 3, 2, 3, 4, 3, 2, 3, 4, 5, 4, 3, 4, 3, 2
  0, 1, 2, 1, 2, 3, 4, 3, 2, 3, 4, 3, 4, 5, 4, 3, 2
  0, 1, 2, 1, 2, 3, 2, 1, 2, 3, 4, 3, 4, 5, 4, 3, 2
  0, 1, 2, 3, 2, 1, 2, 3, 2, 3, 4, 5, 4, 3, 4, 3, 2
  0, 1, 2, 1, 2, 3, 2, 1, 2, 3, 4, 3, 2, 3, 2, 1, 2
  0, 1, 2, 3, 2, 1, 2, 3, 2, 3, 4, 3, 2, 1, 2, 3, 2
  0, 1, 2, 3, 2, 3, 4, 3, 2, 1, 2, 3, 2, 3, 4, 3, 2
  0, 1, 2, 1, 2, 3, 4, 3, 2, 3, 2, 1, 2, 3, 4, 3, 2
  0, 1, 2, 3, 2, 3, 4, 3, 2, 3, 4, 5, 4, 3, 4, 3, 2

Antti Karttunen, Table of n, a(n) for n = 0..8255; the first 128 antidiagonals of array

Transpose of A268833.

A101080[n_, k_]:= DigitCount[BitXor[n, k], 2, 1];A003188[n_]:=BitXor[n, Floor[n/2]]; A006068[n_]:=If[n<2, n, Block[{m=A006068[Floor[n/2]]}, 2m + Mod[Mod[n,2] + Mod[m, 2], 2]]]; a[r_, 0]:= 0; a[0, c_]:=c; a[r_, c_]:= A003188[1 + A006068[a[r - 1, c - 1]]]; A[r_, c_]:=A101080[c, a[r, r + c]]; Table[A[r - c, c], {r, 0, 20}, {c, 0, r}] // Flatten (* Indranil Ghosh, Apr 02 2017 *)

b(n) = if(n<1, 0, b(n\2) + n%2);
A101080(n, k) = b(bitxor(n, k));
A003188(n) = bitxor(n, n\2);
A006068(n) = if(n<2, n, {my(m = A006068(n\2)); 2*m + (n%2 + m%2)%2});
A268820(r, c) = if(r==0, c, if(c==0, 0, A003188(1 + A006068(A268820(r - 1, c - 1)))));
A(r, c) = A101080(c, A268820(r, r + c));
for(r=0, 20, for(c=0, r, print1(A(r - c, c),", ");); print();) \\ Indranil Ghosh, Apr 02 2017

def A101080(n, k): return bin(n^k)[2:].count("1")
def A003188(n): return n^(n//2)
def A006068(n):
    if n<2: return n
    else:
        m=A006068(n//2)
        return 2*m + (n%2 + m%2)%2
def A268820(r, c): return c if r<1 else 0 if c<1 else A003188(1 + A006068(A268820(r - 1, c - 1)))
def a(r, c): return A101080(c, A268820(r, r + c))
for r in range(0, 21):
    print([a(r - c, c) for c in range(0, r + 1)]) # Indranil Ghosh, Apr 02 2017

(define (A268834 n) (A268833bi (A025581 n) (A002262 n))) ;; Code for A268833bi given in A268833.

A261349 T(n,k) is the decimal equivalent of a code for k that maximizes the sum of the Hamming distances between (cyclical) adjacent code words; triangle T(n,k), n>=0, 0<=k<=2^n-1, read by rows.

Original entry on oeis.org

0, 0, 1, 0, 3, 1, 2, 0, 7, 1, 6, 3, 4, 2, 5, 0, 15, 1, 14, 3, 12, 2, 13, 6, 9, 7, 8, 5, 10, 4, 11, 0, 31, 1, 30, 3, 28, 2, 29, 6, 25, 7, 24, 5, 26, 4, 27, 12, 19, 13, 18, 15, 16, 14, 17, 10, 21, 11, 20, 9, 22, 8, 23, 0, 63, 1, 62, 3, 60, 2, 61, 6, 57, 7, 56, 5

Offset: 0

Alois P. Heinz, Nov 18 2015

This code might be called "Anti-Gray code".

The sum of the Hamming distances between (cyclical) adjacent code words of row n gives 0, 2, 6, 20, 56, 144, 352, ... = A014480(n-1) for n>1.

			Triangle T(n,k) begins:
  0;
  0,  1;
  0,  3, 1,  2;
  0,  7, 1,  6, 3,  4, 2,  5;
  0, 15, 1, 14, 3, 12, 2, 13, 6,  9, 7,  8, 5, 10, 4, 11;
  0, 31, 1, 30, 3, 28, 2, 29, 6, 25, 7, 24, 5, 26, 4, 27, 12, 19, ... ;
  0, 63, 1, 62, 3, 60, 2, 61, 6, 57, 7, 56, 5, 58, 4, 59, 12, 51, ... ;

Alois P. Heinz, Rows n = 0..13, flattened
Wikipedia, Gray code
Wikipedia, Hamming distance

Columns k=0-3 give: A000004, A000225, A000012 (for n>1), A000918 (for n>1).
Row lengths give A000079.
Row sums give A006516.
Cf. A003188, A014480, A083329, A083420, A101080.

g:= n-> Bits[Xor](n, iquo(n, 2)):
T:= (n, k)-> (t-> `if`(m=0, t, 2^n-1-t))(g(iquo(k, 2, 'm'))):
seq(seq(T(n, k), k=0..2^n-1), n=0..6);

T(n,k) = A003188(k/2) if k even, T(n,k) = 2^n-1-A003188((k-1)/2) else.
A101080(T(n,2k),T(n,2k+1)) = n, A101080(T(n,2k),T(n,2k-1)) = n-1.
T(n,2^n-1) = A083329(n-1) for n>0.
T(n,2^n-2) = A000079(n-2) for n>1.
T(2n,2n) = A003188(n).
T(2n+1,2n+1) = 2*4^n - 1 - A003188(n) = A083420(n) - A003188(n).

A362951 a(n) is the Hamming distance between the binary expansions of n and phi(n) where phi is the Euler totient function (A000010).

Original entry on oeis.org

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

Offset: 1

Darío Clavijo, Jul 05 2023

a(2^k) = 2 for k >= 1.

a(p) = 1 for each odd prime p because phi(p) = p-1 and (p-1 xor p) = 1.

Paolo Xausa, Table of n, a(n) for n = 1..10000

Cf. A000010, A000120, A065091, A101080, A169814.

A362951[n_] := DigitCount[BitXor[n, EulerPhi[n]], 2, 1];
Array[A362951, 100] (* Paolo Xausa, Feb 20 2024 *)

from gmpy2 import mpz, hamdist
from sympy import totient
a = lambda n: hamdist(mpz(n), mpz(totient(n)))
print([a(n) for n in range(1, 87)])

from sympy import totient
def A362951(n): return (n^totient(n)).bit_count() # Chai Wah Wu, Jul 07 2023

a(n) = A101080(n,A000010(n)).

a(n) = A000120(A169814(n)).

cp's OEIS Frontend

A261075 Semiprimes whose prime factors are of equal binary length and which differ from each other in exactly three bit positions.

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A261077 Semiprimes whose prime factors differ from each other in one bit position only.

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A260737 Sum of Hamming distances between binary representations of prime factors of n, summed over all nonordered pairs of primes present (with multiplicity) in the prime factorization of n.

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A268726 Index of the toggled bit between n and A268717(n+1): a(n) = A000523(A003987(n, A268717(1+n))).

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A268727 One-based index of the toggled bit between n and A268717(n+1): a(n) = A070939(A003987(n,A268717(1+n))).

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A268834 Transpose of array A268833.

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A261349 T(n,k) is the decimal equivalent of a code for k that maximizes the sum of the Hamming distances between (cyclical) adjacent code words; triangle T(n,k), n>=0, 0<=k<=2^n-1, read by rows.

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A362951 a(n) is the Hamming distance between the binary expansions of n and phi(n) where phi is the Euler totient function (A000010).

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