OFFSET
1,1
COMMENTS
The abundance of k is defined as the difference between the sum of the aliquot parts of k and k itself.
FORMULA
EXAMPLE
abundance(215) = (sum of aliquot parts of 215) - 215 = 49 - 215 = -166;
abundance(216) = (sum of aliquot parts of 216) - 216 = 384 -216 = 168;
so abundance(215) + abundance(216) = 2.
MAPLE
with(numtheory): a:=proc(n) if sigma(n)+sigma(n+1)-4*n=4 then n end if end proc: seq(a(n), n=1..100000); # Emeric Deutsch, Apr 02 2008
MATHEMATICA
Select[Range[10^6], DivisorSigma[1, #] + DivisorSigma[1, # + 1] - 4 # == 4 &] (* Michael De Vlieger, Feb 02 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Joseph L. Pe, Mar 04 2008
EXTENSIONS
Three more terms from R. J. Mathar and Emeric Deutsch, Apr 01 2008
a(14)-a(28) from Donovan Johnson, Apr 27 2008
STATUS
approved