3,2

M. Gardner, The Last Recreations, Springer, 1997, p. 282.

M. Gardner, The Colossal Book of Mathematics, 2001, p. 209.

Sequence in context: A021203 A077496 A019106 this_sequence A051567 A085850 A062526

Adjacent sequences: A051563 A051564 A051565 this_sequence A051567 A051568 A051569

dead