OFFSET
1,3
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..300
EXAMPLE
If the {s+t} sums are generated by adding 2 terms of an S set consisting of n different entries, then at least 1, at most n(n+1)/2 = A000217(n) distinct values can be obtained. The set of first n phi-values gives results falling between these two extremes. E.g., n=10, A000010: {1,1,2,2,4,2,6,4,6,4,...}. Additions provide {2,3,4,5,6,7,8,10,12}, i.e., 9 different results. Thus a(10)=9.
MATHEMATICA
f[x_] := EulerPhi[x]; t0=Table[Length[Union[Flatten[Table[f[u]+f[w], {w, 1, m}, {u, 1, m}]]]], {m, 1, 75}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Jun 22 2001
STATUS
approved