OFFSET
1,1
COMMENTS
Each term of the sequence marks the start of four consecutive sigma-values for which the sum of the means equals the sum of the extremes.
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..90 (terms < 4*10^12)
EXAMPLE
sigma(2012) + sigma(2015) = 3528 + 2688 = 6216; sigma(2013) + sigma(2014) = 2976 + 3240 = 6216, so 2012 is a term of the sequence.
MATHEMATICA
Select[Range[10^5], DivisorSigma[1, # ] + DivisorSigma[1, # + 3] == DivisorSigma[1, # + 1] + DivisorSigma[1, # + 2] &]
CROSSREFS
KEYWORD
nonn
AUTHOR
Joseph L. Pe, Oct 25 2002
EXTENSIONS
a(6)-a(26) from Donovan Johnson, Feb 01 2009
a(27)-a(30) from Alex Ratushnyak, Jun 29 2013
STATUS
approved