OFFSET
1,2
COMMENTS
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = 2^n - 2^(n-pi(n)) = the total number of subsets minus the number of subsets of the nonprime elements of {1,..,n}, where pi = A000720. - Greg Martin, May 13 2004
MAPLE
with(numtheory): A089820:=n->2^n - 2^(n-pi(n)): seq(A089820(n), n=1..30); # Wesley Ivan Hurt, Sep 19 2014
MATHEMATICA
Table[2^n - 2^(n - PrimePi[n]), {n, 30}] (* Wesley Ivan Hurt, Sep 19 2014 *)
PROG
(Magma) [2^n-2^(n-#PrimesUpTo(n)) : n in [1..30]]; // Wesley Ivan Hurt, Sep 19 2014
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Reinhard Zumkeller, Nov 12 2003
EXTENSIONS
More terms from Wesley Ivan Hurt, Sep 19 2014
STATUS
approved