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 A068773 Alternating sum phi(1) - phi(2) + phi(3) - phi(4) + ... + ((-1)^(n+1))*phi(n). 4
 1, 0, 2, 0, 4, 2, 8, 4, 10, 6, 16, 12, 24, 18, 26, 18, 34, 28, 46, 38, 50, 40, 62, 54, 74, 62, 80, 68, 96, 88, 118, 102, 122, 106, 130, 118, 154, 136, 160, 144, 184, 172, 214, 194, 218, 196, 242, 226, 268, 248, 280, 256, 308, 290, 330, 306, 342, 314, 372, 356 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS FORMULA a(n) = Sum_{k=1..n} (-1)^(k+1)*phi(k). EXAMPLE a(3) = phi(1) - phi(2) + phi(3) = 1 - 1 + 2 = 2. PROG (PARI) a068773(m)=local(s, n); s=0; for(n=1, m, if(n%2==0, s=s-eulerphi(n), s=s+eulerphi(n)); print1(s, ", ")) CROSSREFS Cf. A000010, A067929. Sequence in context: A284010 A278082 A327442 * A234312 A244136 A338212 Adjacent sequences:  A068770 A068771 A068772 * A068774 A068775 A068776 KEYWORD easy,nonn AUTHOR Klaus Brockhaus, Feb 28 2002 STATUS approved

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Last modified November 28 09:15 EST 2020. Contains 338720 sequences. (Running on oeis4.)