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 A054430 Simple self-inverse permutation of natural numbers: List each clump of phi(n) numbers (starting from phi(2) = 1) in reverse order. 2
 1, 3, 2, 5, 4, 9, 8, 7, 6, 11, 10, 17, 16, 15, 14, 13, 12, 21, 20, 19, 18, 27, 26, 25, 24, 23, 22, 31, 30, 29, 28, 41, 40, 39, 38, 37, 36, 35, 34, 33, 32, 45, 44, 43, 42, 57, 56, 55, 54, 53, 52, 51, 50, 49, 48, 47, 46, 63, 62, 61, 60, 59, 58, 71, 70, 69, 68, 67, 66, 65, 64, 79 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS MAPLE ReverseNextPhi_n_elements_permutation(30); with(numtheory, phi); ReverseNextPhi_n_elements_permutation := proc(u) local m, a, n, k, i; a := []; k := 0; for n from 2 to u do m := k + phi(n); for i from 1 to phi(n) do a := [op(a), m]; m := m-1; k := k+1; od; od; RETURN(a); end; MATHEMATICA A[u_]:=Block[{m, a={}, n, k=0, i}, For[n=2, n<=u, n++, m=k + EulerPhi[n]; For[i=1, i<=EulerPhi[n], i++, AppendTo[a, m]; m=m - 1; k = k + 1]]; Return [a]]; A[30] (* Indranil Ghosh, May 23 2017, translated from MAPLE code *) PROG (Python) from sympy import totient def A(u):     a=[]     k=0     for n in xrange(2, u + 1):         m=k + totient(n)         for i in xrange(1, totient(n) + 1):             a+=[m, ]             m-=1             k+=1     return a print A(30) # Indranil Ghosh, May 23 2017, translated from MAPLE code CROSSREFS Maps fractions between A020652/A020653 and A020653/A020652. See also A054429. Sequence in context: A275900 A296007 A277437 * A276572 A204891 A094681 Adjacent sequences:  A054427 A054428 A054429 * A054431 A054432 A054433 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified January 20 14:40 EST 2019. Contains 319333 sequences. (Running on oeis4.)