The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A076666 Numbers n such that sigma(n) + sigma(n+3) = sigma(n+1) + sigma(n+2). 1
 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 (list; graph; refs; listen; history; text; internal format)
 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 Cf. A000203, A055574, A065900, A073500, A099632, A226361, A226475. Sequence in context: A020433 A191421 A250836 * A323470 A309918 A189188 Adjacent sequences:  A076663 A076664 A076665 * A076667 A076668 A076669 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

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 5 09:03 EST 2020. Contains 338944 sequences. (Running on oeis4.)