cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-4 of 4 results.

A163356 Inverse permutation to A163355, related to Hilbert's curve in N x N grid.

Original entry on oeis.org

0, 1, 3, 2, 8, 10, 11, 9, 12, 14, 15, 13, 7, 6, 4, 5, 16, 18, 19, 17, 20, 21, 23, 22, 28, 29, 31, 30, 27, 25, 24, 26, 48, 50, 51, 49, 52, 53, 55, 54, 60, 61, 63, 62, 59, 57, 56, 58, 47, 46, 44, 45, 39, 37, 36, 38, 35, 33, 32, 34, 40, 41, 43, 42, 128, 130, 131, 129, 132, 133
Offset: 0

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Author

Antti Karttunen, Jul 29 2009

Keywords

Links

Crossrefs

Inverse: A163355.
Second and third "powers": A163906, A163916. See also A059252-A059253.
In range [A000302(n-1)..A024036(n)] of this permutation, the number of cycles is given by A163910, number of fixed points seems to be given by A147600(n-1) (fixed points themselves: A163901). Max. cycle sizes is given by A163911 and LCM's of all cycle sizes by A163912.
Cf. A059252, A059253, A059905, A059906.
Cf. also A302844, A302846, A302781.

Programs

  • PARI
    A057300(n) = { my(t=1,s=0); while(n>0, if(1==(n%4),n++,if(2==(n%4),n--)); s += (n%4)*t; n >>= 2; t <<= 2); (s); };
A163356(n) = if(!n,n,my(i = (#binary(n)-1)\2, f = 4^i, d = (n\f)%4, r = (n%f)); (((((2+(i%2))^d)%5)-1)*f) + if(3==d,f-1-A163356(r),A057300(A163356(r)))); \\ Antti Karttunen, Apr 14 2018

Formula

a(0) = 0, and provided that d=1, 2 or 3, then a((d*(4^i))+r) = (((2+(i mod 2))^d mod 5)-1) * [either A024036(i) - a(r), if d is 3, and A057300(a(r)) in other cases].
From Antti Karttunen, Apr 14 2018: (Start)
A059905(a(n)) = A059253(n).
A059906(a(n)) = A059252(n).
a(n) = A000695(A059253(n)) + 2*A000695(A059252(n)).
(End)

Extensions

Links to further derived sequences and a nicer Scheme function & formula added by Antti Karttunen, Sep 21 2009

A302846 Interleave the Gray-coded X and Y-coordinates of 2-dimensional Hilbert's curve in alternate bit-positions: a(n) = A000695(A003188(A059253(n))) + 2*A000695(A003188(A059252(n))).

Original entry on oeis.org

0, 1, 3, 2, 10, 8, 9, 11, 15, 13, 12, 14, 6, 7, 5, 4, 20, 22, 23, 21, 17, 16, 18, 19, 27, 26, 24, 25, 29, 31, 30, 28, 60, 62, 63, 61, 57, 56, 58, 59, 51, 50, 48, 49, 53, 55, 54, 52, 36, 37, 39, 38, 46, 44, 45, 47, 43, 41, 40, 42, 34, 35, 33, 32, 160, 162, 163, 161, 165, 164, 166, 167, 175, 174, 172, 173, 169, 171, 170, 168, 136
Offset: 0

Views

Author

Antti Karttunen, Apr 14 2018

Keywords

Comments

Like in binary Gray code A003188, also in this permutation the binary expansions of a(n) and a(n+1) differ always by just a single bit-position, that is, A000120(A003987(a(n),a(n+1))) = 1 for all n >= 0. Here A003987 computes bitwise-XOR of its two arguments.
When composed with A052330 this gives A302781.

Links

Crossrefs

Cf. A302845 (inverse permutation).
Cf. A000695, A302844, A057300, A059252, A059253, A064706, A163356, A302781.
Cf. also A003188, A163252, A300838 for other permutations satisfying the same condition.

Programs

  • PARI
    A064706(n) = bitxor(n, n>>2);
A057300(n) = { my(t=1,s=0); while(n>0, if(1==(n%4),n++,if(2==(n%4),n--)); s += (n%4)*t; n >>= 2; t <<= 2); (s); };
A163356(n) = if(!n,n,my(i = (#binary(n)-1)\2, f = 4^i, d = (n\f)%4, r = (n%f)); (((((2+(i%2))^d)%5)-1)*f) + if(3==d,f-1-A163356(r),A057300(A163356(r))));
A302846(n) = A064706(A163356(n));

Formula

a(n) = A000695(A003188(A059253(n))) + 2*A000695(A003188(A059252(n))).
a(n) = A064706(A163356(n)) = A003188(A302844(n)).

A302781 Divisor-or-multiple permutation of natural numbers constructed from two-dimensional Hilbert curve (A163357) and Fermi-Dirac primes (A050376).

Original entry on oeis.org

1, 2, 6, 3, 15, 5, 10, 30, 120, 40, 20, 60, 12, 24, 8, 4, 28, 84, 168, 56, 14, 7, 21, 42, 210, 105, 35, 70, 280, 840, 420, 140, 1260, 3780, 7560, 2520, 630, 315, 945, 1890, 378, 189, 63, 126, 504, 1512, 756, 252, 36, 72, 216, 108, 540, 180, 360, 1080, 270, 90, 45, 135, 27, 54, 18, 9, 117, 351, 702, 234, 936, 468
Offset: 0

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Author

Antti Karttunen, Apr 14 2018

Keywords

Comments

Note that the starting offset is 0, to align with A052330 and A207901.
Shares with A064736, A207901, A298480, A302350, A302783, A303771, etc. the property that a(n) is either a divisor or a multiple of a(n+1). Permutations satisfying such property are called "divisor-or-multiple permutations" in the OEIS, although Mazet & Saias call them "chain permutations" in their paper. [Edited by Antti Karttunen, Aug 26 2018]
One way to construct such permutations is by composing A052330 from the right with any such permutation like A003188 or A302846 where the binary expansions of a(n) and a(n+1) always differ by just a single bit-position.
Further permutations satisfying the same condition could be constructed from higher-dimensional versions (i.e., greater than 2) of Hilbert's space-filling curves, where the coordinates of each dimension would be Gray coded separately and then interleaved together. Permutation A207901 is essentially a one-dimensional variant of the same idea, while this is constructed from the 2-dimensional curve A163357, which is a Hamiltonian path on N X N grid.
See Peter Munn's A300012 for another idea for constructing such a permutation. - Antti Karttunen, Aug 26 2018

Links

Crossrefs

Cf. A302782 (inverse).
Cf. A003188, A050376, A052330, A059252, A059253, A064706, A163356, A163357, A207901, A298480, A300012, A302844, A302846, A302783, A303771.

Programs

  • PARI
    up_to_e = 14;
v050376 = vector(up_to_e);
A050376(n) = v050376[n];
ispow2(n) = (n && !bitand(n,n-1));
i = 0; for(n=1,oo,if(ispow2(isprimepower(n)), i++; v050376[i] = n); if(i == up_to_e,break));
A052330(n) = { my(p=1,i=1); while(n>0, if(n%2, p *= A050376(i)); i++; n >>= 1); (p); };
A064706(n) = bitxor(n, n>>2);
A057300(n) = { my(t=1,s=0); while(n>0, if(1==(n%4),n++,if(2==(n%4),n--)); s += (n%4)*t; n >>= 2; t <<= 2); (s); };
A163356(n) = if(!n,n,my(i = (#binary(n)-1)\2, f = 4^i, d = (n\f)%4, r = (n%f)); (((((2+(i%2))^d)%5)-1)*f) + if(3==d,f-1-A163356(r),A057300(A163356(r))));
A302781(n) = A052330(A064706(A163356(n)));

Formula

a(n) = A052330(A302846(n)), where A302846(n) = A000695(A003188(A059253(n))) + 2*A000695(A003188(A059252(n))).
a(n) = A207901(A302844(n)) = A052330(A064706(A163356(n))).

Extensions

Name edited by Antti Karttunen, Aug 26 2018

A302843 Permutation of nonnegative integers: a(n) = A163355(A006068(n)).

Original entry on oeis.org

0, 1, 2, 3, 12, 13, 14, 15, 10, 9, 8, 11, 4, 7, 6, 5, 26, 27, 24, 25, 30, 29, 28, 31, 16, 19, 18, 17, 22, 23, 20, 21, 42, 43, 40, 41, 46, 45, 44, 47, 32, 35, 34, 33, 38, 39, 36, 37, 58, 57, 56, 59, 52, 55, 54, 53, 48, 49, 50, 51, 60, 61, 62, 63, 192, 193, 194, 195, 204, 205, 206, 207, 202, 201, 200, 203, 196, 199, 198, 197, 218, 219, 216, 217, 222
Offset: 0

Views

Author

Antti Karttunen, Apr 14 2018

Keywords

Links

Crossrefs

Cf. A302844 (inverse).
Cf. A003188, A006068, A057300, A163355, A302845.

Programs

  • PARI
    A006068(n)= { my(s=1, ns); while(1, ns = n >> s; if(0==ns, break()); n = bitxor(n, ns); s <<= 1; ); return (n); } \\ From A006068
A057300(n) = { my(t=1, s=0); while(n>0,  if(1==(n%4),n++,if(2==(n%4),n--)); s += (n%4)*t; n >>= 2; t <<= 2); (s); };
A163355(n) = if(!n,n,my(i = (#binary(n)-1)\2, f = 4^i, d = (n\f)%4, r = (n%f)); if(((1==d)&&!(i%2))||((2==d)&&(i%2)), f+A163355(A057300(r)), if(3==d,f+f+A163355(A057300(r)), (3*f)+A163355(f-1-r))));
A302843(n) = A163355(A006068(n));

Formula

a(n) = A163355(A006068(n)).
a(n) = A302845(A003188(n)).
Showing 1-4 of 4 results.

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