OFFSET
1,4
MATHEMATICA
a = {1}; d = 2; k = 1; Do[ While[ Position[a, d] != {}, d++ ]; k = k + d; d++; a = Append[a, k], {n, 1, 55} ]; b = Table[ n(n + 1)/2, {n, 1, 56} ]; a-b
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Robert G. Wilson v, Nov 14 2001
EXTENSIONS
Corrected definition by Omar E. Pol, Dec 24 2008
STATUS
approved