OFFSET
1,1
MATHEMATICA
Map[EulerPhi, (# (# + 1))/2 & /@ Select[2^Range[100] - 1, PrimeQ]] (* Michael De Vlieger, Jul 25 2015, after Harvey P. Dale at A000396 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Carl Schildkraut, Jul 12 2015
STATUS
approved