OFFSET
1,2
COMMENTS
Sequence is not increasing: a(20)=135 and a(21)=131. Difference in the number of lattice points under the curve xy = n(n+1)/2 and xy = n(n-1)/2. - Emeric Deutsch, Aug 03 2005
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
MAPLE
with(numtheory): a:=n->add(tau(j), j=n*(n-1)/2+1..n*(n+1)/2): seq(a(n), n=1..64); # Emeric Deutsch, Aug 03 2005
MATHEMATICA
Module[{nn=60, ds}, ds=DivisorSigma[0, Range[(nn(nn+1))/2]]; Table[Total[ Take[ ds, {(n(n-1))/2+1, (n(n+1))/2}]], {n, nn}]] (* Harvey P. Dale, Mar 14 2014 *)
With[{nn=60}, Total/@TakeList[DivisorSigma[0, Range[(nn(nn+1))/2]], Range[ nn]]] (* Harvey P. Dale, Mar 29 2022 *)
PROG
(PARI) a(n) = sum(k=n*(n-1)/2+1, n*(n+1)/2, numdiv(k)); \\ Michel Marcus, Aug 20 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Dec 04 2003
EXTENSIONS
Corrected and extended by Emeric Deutsch, Aug 03 2005
STATUS
approved