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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

Table of n, a(n) for n=1..36.

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

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Last modified January 20 21:49 EST 2021. Contains 340332 sequences. (Running on oeis4.)