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G. T. Gilbert, M. I. Krusemeyer and L. C Larson, The Wohascum Problem Book, Math. Assoc of America, 1993, Problem 103, p. 25; Solution, pp. 163-164.
Table of n, a(n) for n=0..30.
Sequence in context: A117515 A085865 A061296 * A218058 A207136 A065410
Adjacent sequences: A019990 A019991 A019992 * A019994 A019995 A019996
R. K. Guy (computed by Marc Paulhus).