OFFSET
1,1
COMMENTS
m*a(n) = A094529(k) for all m>0 and some k.
EXAMPLE
Set of divisors of 440: {1,2,4,5,8,10,11,20,22,40,44,55,88,110,220,440}, there is only one arithmetic progression containing at least four terms: {2,5,8,11} = (2+k*3:0<=k<3), therefore 440 is a term.
MATHEMATICA
oap4Q[n_]:=Length[Select[Subsets[Divisors[n], {4}], Length[Union[ Differences[ #]]]==1&]]==1; Select[Range[102000], oap4Q] (* Harvey P. Dale, Aug 02 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, May 07 2004
STATUS
approved