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

Author

M. F. Hasler, Oct 20 2008

Keywords

• more
• nice
• nonn

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<