OFFSET
1,1
COMMENTS
Sum_{k=1..j} d(k) = Sum_{k=1..j} floor(j/k) = A006218(j).
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..10000
EXAMPLE
9 is in the sequence because the number of divisors of 1,2,...,9 are 1,2,2,3,2,4,2,4,3, respectively, having as sum the prime number 23.
MAPLE
with(numtheory): a:=proc(n) if isprime(sum(tau(k), k=1..n))=true then n else end if end proc: seq(a(n), n=1..400); # Emeric Deutsch, Jun 08 2008
MATHEMATICA
Position[Accumulate@ DivisorSigma[0, Range@ 400], _?PrimeQ][[All, 1]] (* Michael De Vlieger, Feb 19 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, May 12 2008
EXTENSIONS
More terms from Emeric Deutsch, Jun 08 2008
STATUS
approved