cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A353660 The binary expansions of A352909(n+1, 1) and A352909(n+1, 2) encode respectively the 1's and the 2's in the ternary expansion of a(n).

Original entry on oeis.org

0, 2, 1, 6, 3, 8, 7, 5, 4, 18, 9, 20, 19, 11, 10, 24, 21, 15, 12, 26, 25, 23, 22, 17, 16, 14, 13, 54, 27, 56, 55, 29, 28, 60, 57, 33, 30, 62, 61, 59, 58, 35, 34, 32, 31, 72, 63, 45, 36, 74, 73, 65, 64, 47, 46, 38, 37, 78, 75, 69, 66, 51, 48, 42, 39, 80, 79, 77
Offset: 0

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Author

Rémy Sigrist, May 02 2022

Keywords

Comments

This sequence is a permutation of the nonnegative integers with inverse A353661.

Examples

			For n = 42:
- A352909(43, 1) = 9,
- A352909(43, 2) = 2,
- the binary expansion of 9 is "1001",
- the binary expansion of 2 is "10",
- so the ternary expansion of a(42) is "1021",
- and a(42) = 34.
		

Crossrefs

Cf. A005836, A352909, A353661 (inverse), A353662.

Programs

  • PARI
    b2t(n) = fromdigits(binary(n), 3)
    { n=-1; for (d=0, 2^8-1, for (k=0, d, if (bitand(t1=k, t2=d-k)==0, print1 (b2t(t1) + 2*b2t(t2)", "); if (n++==67, break (2))))) }

Formula

a(n) = A005836(A352909(n+1, 1)) + 2*A005836(A352909(n+1, 2)).
a(n) < 3^k iff n < 3^k.
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