OFFSET
0,2
COMMENTS
See comment section of A037202.
a(n) ~ 2*a(n-1).
FORMULA
Also PrimePi( A037231 ).
MATHEMATICA
a[1] = 1; a[n_] := a[n] = 1 + Plus @@ (a@ PrimePi@# & /@ First /@ FactorInteger[ Prime@ n - 1]); k = 1; t = Table[0, {1000}]; While[k < 1000000000000001, If[a@ k < 1001 && t[[a[k]/2]] == 0, t[[a[k]/2]] = k; Print[{a@k, k}]]; k++]; t
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Joerg Arndt and Robert G. Wilson v, Jul 02 2014
STATUS
approved