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!)
 A231546 Numbers n such that sigma(n) = sigma(n-1). 8
 15, 207, 958, 1335, 1365, 1635, 2686, 2975, 4365, 14842, 18874, 19359, 20146, 24958, 33999, 36567, 42819, 56565, 64666, 74919, 79827, 79834, 84135, 92686, 109215, 111507, 116938, 122074, 138238, 147455, 161002, 162603, 166935, 174718, 190774, 193894, 201598 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also, numbers n such that n = antisigma(n) - antisigma(n-1), where antisigma(n) = A024816(n) = the sum of the non-divisors of n that are between 1 and n. LINKS Hugo Pfoertner, Table of n, a(n) for n = 1..550 FORMULA a(n) = A002961(n) + 1. EXAMPLE 15 = antisigma(15) - antisigma(14) = 96 - 81. PROG (PARI) n=0; sp=sigma(2); for(k=3, oo, my(s=sigma(k)); if(s==sp, print1(k, ", "); n++; if(n>36, break)); sp=s) \\ Hugo Pfoertner, Mar 06 2020 CROSSREFS Cf. A002961, A024816 (antisigma(n)), A231545 (numbers n such that antisigma(n) = antisigma(n-1)). Sequence in context: A075280 A093747 A061637 * A063906 A194481 A078265 Adjacent sequences:  A231543 A231544 A231545 * A231547 A231548 A231549 KEYWORD nonn AUTHOR Jaroslav Krizek, Nov 11 2013 EXTENSIONS More terms from Hugo Pfoertner, Mar 06 2020 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 November 24 01:40 EST 2020. Contains 338603 sequences. (Running on oeis4.)