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Search: id:A067929
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| A067929 |
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Numbers n such that n divides the alternating sum phi(1)-phi(2)+phi(3)-phi(4)+...+((-1)^(n+1))phi(n). |
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+0
2
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| 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
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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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.
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MATHEMATICA
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s = 0; Do[s = s + (-1)^(i + 1) * EulerPhi[i]; If[ Mod[s, i] == 0, Print[i]], {i, 1, 10^7}]
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PROGRAM
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(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, ", ")))}
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CROSSREFS
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Cf. A000010, A068773.
Sequence in context: A097001 A085931 A125885 this_sequence A064361 A064407 A052289
Adjacent sequences: A067926 A067927 A067928 this_sequence A067930 A067931 A067932
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KEYWORD
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nonn
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AUTHOR
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Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Feb 22 2002
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EXTENSIONS
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Edited and extended by Robert G. Wilson v (rgwv(AT)rgwv.com) and Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Feb 27 2002
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