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 A101299 Numbers n such that -1 + Sum_{x=1..n} phi(x) is a prime number. 0
 3, 4, 6, 7, 10, 11, 15, 16, 18, 20, 21, 22, 24, 25, 26, 27, 28, 29, 30, 31, 34, 35, 37, 38, 42, 50, 52, 53, 64, 65, 66, 70, 77, 79, 83, 91, 105, 113, 116, 126, 127, 128, 130, 132, 133, 135, 138, 141, 144, 150, 152, 157, 159, 161, 164, 168, 189, 198, 224, 225, 231, 241 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..62. EXAMPLE 3 = phi(1)+phi(2)+phi(3)-1 ==> 3, a prime, so 3 is a term. 5 = phi(1)+phi(2)+phi(3)+phi(4)-1 ==> 4, not a prime, so 5 is not a term. MAPLE with(numtheory): select(n-> isprime(add(phi(x), x=1..n)-1), [\$1..300])[]; # Emeric Deutsch, Jul 20 2005 PROG (PARI) isok(n) = isprime(sum(k=1, n, eulerphi(k))-1); \\ Michel Marcus, Aug 21 2019 CROSSREFS Cf. A002088. Sequence in context: A191926 A065135 A229792 * A143837 A354005 A330172 Adjacent sequences: A101296 A101297 A101298 * A101300 A101301 A101302 KEYWORD nonn,easy AUTHOR Jorge Coveiro, Dec 22 2004 EXTENSIONS More terms from Emeric Deutsch, Jul 20 2005 Name edited by Michel Marcus, Aug 21 2019 STATUS approved

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Last modified December 1 05:26 EST 2023. Contains 367468 sequences. (Running on oeis4.)