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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A067929 Numbers n such that n divides the alternating sum phi(1)-phi(2)+phi(3)-phi(4)+...+((-1)^(n+1))phi(n). 2
 1, 2, 4, 12, 17, 55, 57, 80, 195, 211, 233, 602, 694, 1319, 2726, 26312, 71173, 101457, 145789, 165710, 299228, 483888, 718738, 1757846, 4206121, 9518456, 15505388, 15885915, 15929230, 26445656, 28665696, 37875137, 147389152, 218849960, 430031707, 507418131 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS phi(1)-phi(2)+phi(3)-phi(4) = 1-1+2-2 = 0, which is divisible by 4, so 4 is a term of the sequence. LINKS MATHEMATICA s = 0; Do[s = s + (-1)^(i + 1) * EulerPhi[i]; If[ Mod[s, i] == 0, Print[i]], {i, 1, 10^7}] PROG (PARI) {a067929(m)=local(s, n); s=0; for(n=1, m, if(n%2==0, s=s-eulerphi(n), s=s+eulerphi(n)); if(s%n==0, print1(n, ", ")))} CROSSREFS Cf. A000010, A068773. Sequence in context: A192533 A085931 A125885 * A337837 A064361 A303403 Adjacent sequences:  A067926 A067927 A067928 * A067930 A067931 A067932 KEYWORD nonn AUTHOR Joseph L. Pe, Feb 22 2002 EXTENSIONS Edited and extended by Robert G. Wilson v and Klaus Brockhaus, Feb 27 2002 a(27)-a(36) from Donovan Johnson, Jul 26 2011 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 January 20 21:49 EST 2021. Contains 340332 sequences. (Running on oeis4.)