OFFSET
1,2
FORMULA
a(n) = Sum_{k=n..sigma(n)} k. - Wesley Ivan Hurt, Apr 20 2023
EXAMPLE
a(1)=1=1. a(2)=5=2+3. a(3)=7=3+4. a(4)=22=4+5+6+7. a(5)=11=5+6. a(6)=63=6+7+8+9+10+11+12.
MATHEMATICA
Total[Range[#, DivisorSigma[1, #]]]&/@Range[60] (* Harvey P. Dale, Feb 23 2023 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Juri-Stepan Gerasimov, Jul 04 2009
EXTENSIONS
a(12), a(33), a(34) and others corrected by R. J. Mathar, Jul 06 2009
STATUS
approved