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 A280592 Numbers n such that phi(n) is a Fibonacci number. 3
 1, 2, 3, 4, 6, 15, 16, 20, 24, 30, 185, 219, 273, 285, 292, 296, 304, 315, 364, 370, 380, 432, 438, 444, 456, 468, 504, 540, 546, 570, 630, 3235, 5176, 6470, 7764, 46843, 47423, 47693, 48053, 50431, 52403, 56231, 57965, 59555, 62855, 67655, 67865, 70735, 72123, 72297, 73473 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Note that the sequence of corresponding Fibonacci numbers is not the same as A134492. See also A280681. LINKS Robert Israel, Table of n, a(n) for n = 1..2075 EXAMPLE 24 is a term because phi(24) = 8 is a Fibonacci number. MAPLE fibs:= {seq(combinat:-fibonacci(n), n=1..30)}: N:= combinat:-fibonacci(31): sort(convert(select(t -> t <= N, map(t -> op(numtheory:-invphi(t)), fibs)), list)); # Robert Israel, Nov 20 2019 MATHEMATICA Module[{fibs=Fibonacci[Range[30]]}, Select[Range[80000], MemberQ[ fibs, EulerPhi[ #]]&]] (* Harvey P. Dale, Jul 04 2021 *) PROG (PARI) isFibonacci(n)=my(k=n^2); issquare(k+=(k+1)<<2) || (n>0 && issquare(k-8)); is(n)=isFibonacci(eulerphi(n)); CROSSREFS Cf. A000010, A000045, A134492, A280681. Sequence in context: A049911 A056712 A204540 * A330990 A337129 A002087 Adjacent sequences:  A280589 A280590 A280591 * A280593 A280594 A280595 KEYWORD nonn,look AUTHOR Altug Alkan, Jan 06 2017 STATUS approved

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Last modified November 28 16:25 EST 2021. Contains 349413 sequences. (Running on oeis4.)