A076528 Numbers n such that sigma(n) = sigma(n-1) - sigma(n-2).

955, 1301, 11143, 38215, 89485, 152155, 167785, 254137, 303281, 473317, 574717, 813921, 918081, 1307023, 2008361, 3676243, 9878245, 10368513, 12548755, 19411481, 22493263, 42413485, 77766487, 81513817, 157874001, 240828973

Offset: 1

Author

Joseph L. Pe, Oct 18 2002

Keywords

• nonn

Examples

			sigma(955) = 1152 sigma(954) = 2106 sigma(953) = 954 and 1152 = 2106 - 954; hence 955 is a term of the sequence.
		

Links

• Giovanni Resta, Table of n, a(n) for n = 1..170 (terms < 10^13)

Crossrefs

Cf. A000203, A073500.

Programs

Mathematica

Select[Range[3, 10^5], DivisorSigma[1, # ] == DivisorSigma[1, # - 1] - DivisorSigma[1, # - 2] &]
Flatten[Position[Partition[DivisorSigma[1,Range[37*10^5]],3,1],?(#[[3]]==#[[2]]-#[[1]]&),1,Heads->False]]+2 (* The program generates the first 16 terms of the sequence. *) (* _Harvey P. Dale, May 23 2025 *)

Formula

a(n) = A073500(n)+1 - Alex Ratushnyak, Jul 06 2013.

Extensions

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