1,2
R. K. Guy, Unsolved Problems in Number Theory, D3.
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.
Sequence in context: A127726 A117063 A178911 * A076233 A066581 A054776
Adjacent sequences: A001216 A001217 A001218 * A001220 A001221 A001222
nonn,fini,full
N. J. A. Sloane (njas(AT)research.att.com).