OFFSET
1,1
COMMENTS
Also the sum of the primes between 10^(n-1) and 10^n.
a(12) to a(20) were computed from A046731(12)-A046731(11) to A046731(20)-A046731(19). - Cino Hilliard, May 31 2008
A good estimate for the sum of the primes < k is k^2/(2*log(k)-1). Using this formula, a(20)~(10^20)^2/(2*log(10^20)-1) -(10^19)^2/(2*log(10^19)-1) = 108609290005707493265628731014013409909. The relative error this formula produces for the last 5 terms is a(16): -0.00019454, a(17): -0.00017176, a(18): -0.00015275, a(19): -0.00013674, a(20): -0.00012312. - Cino Hilliard, May 31 2008
LINKS
Hugo Pfoertner, Table of n, a(n) for n = 1..26 (terms 1..20 from Cino Hilliard).
Cino Hilliard, Count,Sum primes in a range Win32 Gcc+Gmp.
FORMULA
EXAMPLE
a(1) = 2 + 3 + 5 + 7 = 17, sum of four 1-digit primes.
MAPLE
a:=proc(n) local tot, b, j: tot:=nextprime(10^(n-1)): b:=nextprime(10^(n-1)): for j while nextprime(b) < 10^n do tot:=tot+nextprime(b): b:=nextprime(b) end do:tot end proc: # Emeric Deutsch, Oct 08 2007
MATHEMATICA
Prepend[Table[Apply[Plus, Table[Prime[w], {w, PrimePi[10^(n-1)]+1, PrimePi[10^n]}]], {n, 2, 7}], 17] (* corrected by Ivan N. Ianakiev, Aug 12 2016 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Labos Elemer, Nov 18 2002
EXTENSIONS
2 more terms from Lior Manor, Sep 11 2007
Corrected and extended by Emeric Deutsch, Oct 08 2007
More terms from Cino Hilliard, May 31 2008
STATUS
approved