OFFSET
0,1
COMMENTS
Of the terms n <= 66, all are semiprimes except those for n = 0, 1, 5, and 19. Why? - T. D. Noe, Oct 17 2013
LINKS
T. D. Noe, Table of n, a(n) for n = 0..66
MATHEMATICA
nn = 34; t = Table[0, {nn}]; found = 0; n = 0; While[found < nn, n++; len = Length[NestWhileList[EulerPhi[#] + 1 &, n, UnsameQ, All]] - 2; If[len <= nn && t[[len]] == 0, t[[len]] = n; found++]]; t = Join[{2}, t] (* T. D. Noe, Oct 17 2013 *)
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
STATUS
approved