This site is supported by donations to The OEIS Foundation.

 Annual appeal: Please make a donation to keep the OEIS running! Over 6000 articles have referenced us, often saying "we discovered this result with the help of the OEIS". Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A160691 a(n) = the number of divisors of A160689(n) = the number of divisors of A160690(n). 5
 1, 2, 2, 2, 4, 2, 2, 4, 2, 2, 4, 2, 2, 4, 2, 4, 2, 4, 4, 4, 2, 4, 4, 4, 2, 4, 6, 4, 6, 2, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 2, 2, 4, 4, 4, 2, 4, 4, 2, 4, 2, 4, 4, 4, 2, 2, 4, 4, 2, 4, 4, 4, 2, 4, 2, 4, 4, 2, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 2, 2, 4, 2, 4, 4, 2, 4, 4, 4, 4, 4, 4, 4, 4, 2, 4, 2, 4, 4, 2, 4, 4, 2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS From Farideh Firoozbakht, May 28 2009: (Start) For the first 200000 natural numbers n, a(n) is in the set {1,2,4,6,8,12} and in fact we have: For one number n, a(n)=1. For 13 numbers n, a(n)=12 (see the sequence A158963). For 4785 numbers n, a(n)=6. For 6706 numbers n, a(n)=8. For 26790 numbers n, a(n)=2. For 161705 numbers n, a(n)=4. Also n=2 is the only number (less than 200000) such that a(n) = a(n+1) = a(n+2) = 2. And for the 53 consecutive numbers 64833, 64834, ..., 64885 we have a(n)=4. (End) a(n)=10 for n=271532 and n=424519 (up to 5*10^5). - Michel Marcus, Sep 05 2017 LINKS Michel Marcus, Table of n, a(n) for n = 1..5000 MATHEMATICA c[1] = 1; c[n_] := c[n] = (s = Sum[c[k], {k, n - 1}]; For[m = 1, DivisorSigma[0, m] != DivisorSigma[0, s + m], m++]; m); a[n_] := a[n] = DivisorSigma[0, c[n]]; Table[a[n], {n, 105}] (* Farideh Firoozbakht, May 28 2009 *) PROG (PARI) lista(nn) = {k = 1; print1(numdiv(k), ", "); last = k; for (n=2, nn, k = last+1; while(numdiv(k) != numdiv(k - last), k++); print1(numdiv(k), ", "); s += k; last = k; ); } \\ Michel Marcus, Sep 05 2017 CROSSREFS Cf. A160689, A160690. Cf. A158963, A158964. [Farideh Firoozbakht, May 28 2009] Sequence in context: A075016 A279409 A102445 * A049716 A188903 A066671 Adjacent sequences:  A160688 A160689 A160690 * A160692 A160693 A160694 KEYWORD nonn AUTHOR Leroy Quet, May 24 2009 EXTENSIONS More terms from Farideh Firoozbakht, May 28 2009 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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.