A076666 Numbers n such that sigma(n) + sigma(n+3) = sigma(n+1) + sigma(n+2).

2012, 2096, 15892, 17888, 39916, 102784, 141008, 146227, 482144, 487865, 1321312, 1887008, 2749057, 3513881, 7141158, 16767172, 17503912, 28122834, 30534728, 37453779, 42140437, 60994100, 67777337, 78251933, 113091820, 113768920, 129868059, 199240914, 240859196, 302897372

Offset: 1

Author

Joseph L. Pe, Oct 25 2002

Keywords

• nonn

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.

Examples

			sigma(2012) + sigma(2015) = 3528 + 2688 = 6216; sigma(2013) + sigma(2014) = 2976 + 3240 = 6216, so 2012 is a term of the sequence.
		

Links

• Giovanni Resta, Table of n, a(n) for n = 1..90 (terms < 4*10^12)

Crossrefs

Cf. A000203, A055574, A065900, A073500, A099632, A226361, A226475.

Programs

Mathematica

Select[Range[10^5], DivisorSigma[1, # ] + DivisorSigma[1, # + 3] == DivisorSigma[1, # + 1] + DivisorSigma[1, # + 2] &]

Extensions

a(6)-a(26) from Donovan Johnson, Feb 01 2009

a(27)-a(30) from Alex Ratushnyak, Jun 29 2013