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 A180643 Numbers n such that 1+phi(n)^2 is prime. Phi is the Euler totient function. 1
 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 17, 18, 22, 25, 32, 33, 34, 35, 37, 39, 40, 41, 44, 45, 48, 50, 52, 55, 56, 57, 60, 63, 66, 67, 70, 72, 74, 75, 76, 78, 81, 82, 84, 87, 88, 90, 100, 108, 110, 114, 116, 121, 126, 127, 129, 131, 132, 134, 143, 147, 150, 151, 155 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..2800 EXAMPLE a(20)=34 since 1+phi(34)^2 = 1+16^2 = 257 is prime. MAPLE select(t -> isprime(numtheory:-phi(t)^2+1), [\$1..1000]); # Robert Israel, Mar 11 2020 MATHEMATICA Select[Range[200], PrimeQ[1+EulerPhi[#]^2]&] (* Harvey P. Dale, Aug 13 2014 *) PROG (PARI) isok(n) = isprime(1 + eulerphi(n)^2) \\ Michel Marcus, Jul 18 2013 CROSSREFS Cf. A000010, A127435 (primes in this sequence). Sequence in context: A096902 A246081 A117325 * A017905 A333598 A044962 Adjacent sequences: A180640 A180641 A180642 * A180644 A180645 A180646 KEYWORD nonn AUTHOR Carmine Suriano, Sep 14 2010 STATUS approved

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Last modified September 19 14:26 EDT 2024. Contains 376012 sequences. (Running on oeis4.)