A066244 Numbers n such that sigma(n+2)-2sigma(n+1)+sigma(n) = n.

2, 38, 66290, 113978, 9121109348

Offset

1,1

Comments

The equation here is the difference equation (applied to sigma) corresponding to the differential equation y" = x (Hooke's law with constant = -1).

a(6) > 10^13. - Giovanni Resta, Jul 13 2015

Links

Table of n, a(n) for n=1..5.

Example

sigma(40)-2*sigma(39)+sigma(38) = 90 - 2*56 + 60 = 38, so 38 is a term of the sequence.

Mathematica

Select[Range[1, 10^6], DivisorSigma[1, # + 2] - 2*DivisorSigma[1, # + 1] + DivisorSigma[1, # ] == # &]

Crossrefs

Sequence in context: A348162 A132396 A263374 * A055689 A345316 A028442

Adjacent sequences: A066241 A066242 A066243 * A066245 A066246 A066247

Keyword

more,nonn

Author

Joseph L. Pe, Dec 19 2001

Extensions

a(5) from Donovan Johnson, Feb 01 2009

Status

approved