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A119257 A permutation of the positive integers formed by reversing the order of the composites within each run of composites (1 and primes are left alone). 1
1, 2, 3, 4, 5, 6, 7, 10, 9, 8, 11, 12, 13, 16, 15, 14, 17, 18, 19, 22, 21, 20, 23, 28, 27, 26, 25, 24, 29, 30, 31, 36, 35, 34, 33, 32, 37, 40, 39, 38, 41, 42, 43, 46, 45, 44, 47, 52, 51, 50, 49, 48, 53, 58, 57, 56, 55, 54, 59, 60, 61, 66, 65, 64, 63, 62, 67, 70, 69, 68, 71, 72 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..20000

Index entries for sequences that are permutations of the natural numbers

FORMULA

a(n) = Sum_{k=1..2n} floor(cos^2(Pi*(n-1)!^(k-1)/(k-1)!)) - Sum_{k=1..n} floor(cos^2(Pi*(k-1)!^n/n!)). - Anthony Browne, May 24 2016

EXAMPLE

The run of composites (24,25,26,27,28) becomes (28,27,26,25,24).

MATHEMATICA

Block[{$MaxExtraPrecision = 1000}, Table[Sum[Floor[Cos[Pi (n - 1)!^(k - 1)/(k - 1)!]^2], {k, 2 n}] - Sum[ Floor[Cos[Pi (k - 1)!^n/n!]^2], {k, n}], {n, 72}]] (* Michael De Vlieger, May 24 2016 *)

PROG

(PARI) {m=73; print1(1, ", "); n=2; while(n<=m, while(isprime(n), print1(n, ", "); n++); k=n; while(!isprime(n), n++); forstep(a=n-1, k, -1, print1(a, ", ")))} \\ Klaus Brockhaus, Aug 16 2006

CROSSREFS

Sequence in context: A072794 A181820 A199426 * A266645 A266646 A102455

Adjacent sequences:  A119254 A119255 A119256 * A119258 A119259 A119260

KEYWORD

nonn

AUTHOR

Leroy Quet, Jul 23 2006

EXTENSIONS

More terms from Klaus Brockhaus, Aug 16 2006

STATUS

approved

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Last modified January 23 15:15 EST 2021. Contains 340385 sequences. (Running on oeis4.)