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.

A145768 a(n) = the bitwise XOR of squares of first n natural numbers.

Original entry on oeis.org

0, 1, 5, 12, 28, 5, 33, 16, 80, 1, 101, 28, 140, 37, 225, 0, 256, 33, 357, 12, 412, 37, 449, 976, 400, 993, 325, 924, 140, 965, 65, 896, 1920, 961, 1861, 908, 1692, 965, 1633, 912, 1488, 833, 1445, 668, 1292, 741, 2721, 512, 2816, 609, 2981, 396, 2844, 485
Offset: 0

Views

Author

Vladimir Reshetnikov, Oct 18 2008

Keywords

Comments

Up to n=10^8, a(15) is the only zero term and a(1)=a(9) are the only terms for which a(n)=1. Can it be proved that any number can only appear a finite number of times in this sequence? [M. F. Hasler, Oct 20 2008]
Even terms occur at A014601, odd terms at A042963; A010873(a(n))=A021913(n+1). - Reinhard Zumkeller, Jun 05 2012
If squares occur, they must be at indexes != 2 or 5 (mod 8). - Roderick MacPhee, Jul 17 2017

Crossrefs

Programs

  • Haskell
    import Data.Bits (xor)
    a145768 n = a145768_list !! n
    a145768_list = scanl1 xor a000290_list  -- Reinhard Zumkeller, Jun 05 2012
    
  • Maple
    A[0]:= 0:
    for n from 1 to 100 do A[n]:= Bits:-Xor(A[n-1],n^2) od:
    seq(A[i],i=0..100); # Robert Israel, Dec 08 2019
  • Mathematica
    Rest@ FoldList[BitXor, 0, Array[#^2 &, 50]]
  • PARI
    an=0; for( i=1,50, print1(an=bitxor(an,i^2),",")) \\ M. F. Hasler, Oct 20 2008
    
  • PARI
    al(n)=local(m);vector(n,k,m=bitxor(m,k^2))
    
  • Python
    from functools import reduce
    from operator import xor
    def A145768(n):
        return reduce(xor, [x**2 for x in range(n+1)]) # Chai Wah Wu, Aug 08 2014

Formula

a(n)=1^2 xor 2^2 xor ... xor n^2.

A145828 Squares in A145768 (XOR of squares of the numbers 1...n).

Original entry on oeis.org

0, 1, 16, 1, 225, 0, 256, 400, 961, 256, 2401, 4225, 50176, 9216, 9216, 113569, 20736, 518400, 160000, 893025, 390625, 861184, 685584, 134689, 861184, 3568321, 389376, 6806881, 12730624, 12730624, 4260096, 105534529
Offset: 1

Views

Author

M. F. Hasler, Oct 20 2008

Keywords

Crossrefs

Equals A145768 intersect A000290; a(n) = A145768(A145827(n)) = A145829(n)^2.

Programs

  • Mathematica
    Reap[For[Sow[x=0]; k=1, k <= 10^4, k++, x = BitXor[x, k^2]; If[IntegerQ[ Sqrt[x]], Sow[x]]]][[2, 1]] (* Jean-François Alcover, Nov 25 2015 *)
  • PARI
    an=0; for( i=1,10^4, an=bitxor(an,i^2); issquare(an) && print1(an","))
    
  • PARI
    {a(n) = my(x, m, k); while( mMichael Somos, Aug 05 2014 */
  • Python
    from gmpy2 import is_square
    filter(is_square, [reduce(lambda x,y:x^y, [x**2 for x in range(n)]) for n in range(1,10**4)]) # Chai Wah Wu, Aug 05 2014
    

Extensions

Edited to start at 0 to match A145768 by Chai Wah Wu, Aug 05 2014

A145830 Indices for which A145768 (XOR of squares of the numbers 1...n) is a power of 2.

Original entry on oeis.org

1, 7, 9, 16, 47, 63
Offset: 1

Views

Author

M. F. Hasler, Oct 20 2008

Keywords

Comments

Next term is > 10^7.
a(7) > 1.5*10^9. [Jon E. Schoenfield, Jan 14 2009]
a(7) > 10^11. [Sean A. Irvine, Aug 12 2010]

Crossrefs

A145830 = A145768 intersect A000079. A145768(a(n)) = 2^A145831(n); See also A145827-A145829.

Programs

  • Mathematica
    Position[ FoldList[ BitXor, 0, Range[10^6]^2], n_ /; IntegerQ[Log[2, n]]] - 1 // Flatten (* Jean-François Alcover, Sep 30 2013 *)
  • PARI
    an=0; for( i=1,10^6, an=bitxor(an,i^2); an & an==1<
    				

A145831 Log_2 ( A145768( A145830(n))).

Original entry on oeis.org

0, 4, 0, 8, 9, 8
Offset: 1

Views

Author

M. F. Hasler, Oct 20 2008

Keywords

Crossrefs

A145830 = A145768 intersect A000079. A145768(A145830(n)) = 2^a(n). See also A145827-A145829.

Programs

  • PARI
    an=0; for( i=1,10^7, an=bitxor(an,i^2); an & an==1<
    				
Showing 1-4 of 4 results.