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

1, 7, 9, 16, 47, 63

Offset

1,2

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

Links

Table of n, a(n) for n=1..6.

Mathematica

Position[ FoldList[ BitXor, 0, Range[10^6]^2], n_ /; IntegerQ[Log[2, n]]] - 1 // Flatten (* Jean-François Alcover, Sep 30 2013 *)

Prog

(PARI) an=0; for(i=1, 10^6, hammingweight(an=bitxor(an, i^2))==1 && print1(i", ")) \\ Code updated, improved and typo fixed (thanks to Bill McEachen) by M. F. Hasler, Sep 24 2025

Crossrefs

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

Sequence in context: A372934 A020691 A366674 * A195563 A250292 A140364

Adjacent sequences: A145827 A145828 A145829 * A145831 A145832 A145833

Keyword

more,nice,nonn

Author

M. F. Hasler, Oct 20 2008

Status

approved