This site is supported by donations to The OEIS Foundation.

 Annual Appeal: Please make a donation to keep the OEIS running. In 2018 we replaced the server with a faster one, added 20000 new sequences, and reached 7000 citations (often saying "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A067816 Numbers n such that sigma(n+1) - sigma(n) = n + 1. 11
 1, 5, 8585, 16119, 29886159 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Mersenne primes are solutions of sigma(x+1) - sigma(x) = x. Numbers n such that antisigma(n) = antisigma(n+1), where antisigma(n) = the sum of the nondivisors of n that are between 1 and n. For example, antisigma(5) = 2 + 3 + 4 = 9; antisigma(6) = 4 + 5 = 9, so 5 is a term of the sequence. - Joseph L. Pe, Oct 22 2002 The next term, if it exists, must be greater than 5*10^8. - Martin Fuller, May 06 2007 a(5), if it exists, is greater than 10^13. - Giovanni Resta, Jul 30 2013 LINKS MATHEMATICA h[n_] := (n (n + 1)/2) - DivisorSigma[1, n]; Select[Range[10^6], h[ # ] == h[ # + 1] &] (* Joseph L. Pe, Oct 22 2002 *) lst = {}; a = b = 1; Do[ a = b; b = DivisorSigma[1, n]; If[a + n == b, Print[n]; AppendTo[lst, n]], {n, 2^31}] (* Robert G. Wilson v, Jun 02 2007 *) CROSSREFS Cf. A024816. Sequence in context: A243235 A145530 * A076629 A052027 A109514 A022918 Adjacent sequences:  A067813 A067814 A067815 * A067817 A067818 A067819 KEYWORD nonn AUTHOR Benoit Cloitre, Feb 08 2002 EXTENSIONS a(5) from Martin Fuller, May 06 2007 Edited by N. J. A. Sloane at the suggestion of Andrew S. Plewe, May 31 2007 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 17 14:50 EST 2018. Contains 318201 sequences. (Running on oeis4.)