A115317 a(n) = A115316(A115316(n)).

1, 2, 6, 8, 4, 5, 10, 3, 12, 14, 9, 11, 16, 7, 18, 20, 15, 17, 22, 13, 24, 25, 21, 26, 23, 19, 27, 28, 29, 30, 31, 32, 33, 34, 36, 37, 35, 43, 41, 38, 42, 39, 40, 53, 47, 44, 61, 45, 46, 71, 48, 59, 57, 49, 50, 63, 51, 52, 89, 67, 54, 68, 55, 56, 74, 73, 58, 107, 60, 79, 113, 62

Offset: 1

Author

Reinhard Zumkeller, Jan 20 2006

Keywords

• nonn

Comments

Inverse integer permutation of A115319;

A115318(a(n)) = a(A115318(n)) = A115316(n).

Links

• Index entries for sequences that are permutations of the natural numbers

Crossrefs

Cf. A115316, A115318, A115319.

Programs

Mathematica

nmax = 72; (* length of this sequence *)
nn = nmax + 20 (* estimated length of A115316 - should be increased if insufficient *);
np = Ceiling[nn/3] + 1;
nc = Ceiling[(2/3) nn];
pp = Prime[Range[np]];
cc = Partition[Select[Range[FindRoot[n == nc + PrimePi[n] + 1, {n, nc, 2nc}][[1, 2]] // Floor], CompositeQ], 2];
A115316 = Join[{1}, Riffle[pp, cc] // Flatten][[1 ;; nn]];
a[n_] := A115316[[A115316[[n]]]];
Table[a[n], {n, 1, nmax}] (* Jean-François Alcover, Nov 15 2021 *)