This site is supported by donations to The OEIS Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A249818 Permutation of natural numbers: a(1) = 1, a(n) = A246278(A055396(n),A078898(n)). 29
 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 27, 22, 23, 24, 25, 26, 21, 28, 29, 30, 31, 32, 45, 34, 35, 36, 37, 38, 33, 40, 41, 42, 43, 44, 81, 46, 47, 48, 49, 50, 75, 52, 53, 54, 125, 56, 63, 58, 59, 60, 61, 62, 39, 64, 55, 66, 67, 68, 135, 70, 71, 72, 73, 74, 51, 76, 77, 78, 79, 80, 99, 82, 83, 84, 175, 86, 105 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n) tells which number in square array A246278 is at the same position where n is in array A083221, the sieve of Eratosthenes. As both arrays have even numbers as their topmost row and primes as their leftmost column, both sequences are among the fixed points of this permutation. Equally: a(n) tells which number in array A246279 is at the same position where n is in the array A083140, as they are the transposes of above two arrays. LINKS Antti Karttunen, Table of n, a(n) for n = 1..10000 FORMULA a(1) = 1, a(n) = A246278(A055396(n), A078898(n)). a(1) = 1, a(n) = A246278(A055396(n), A249822(A055396(n), A246277(n))). As a composition of other permutations: a(1) = 1, and for n > 1, a(n) = 1 + A249816(n-1). Other identities. For all n >= 1: a(A005843(n)) = A005843(n) and a(A000040(n)) = A000040(n). [Fixes even numbers and primes, among other numbers. Cf. comments above]. A020639(a(n)) = A020639(n) and A055396(a(n)) = A055396(n). [Preserves the smallest prime factor of n]. MATHEMATICA lim = 87; a003961[p_?PrimeQ] := a003961[p] = Prime[PrimePi@ p + 1]; a003961 = 1; a003961[n_] :=  a003961[n] = Times @@ (a003961[First@ #]^Last@ # &) /@ FactorInteger@ n; a055396[n_] := PrimePi[FactorInteger[n][[1, 1]]]; a078898 = Block[{nn = 90, spfs}, spfs = Table[FactorInteger[n][[1, 1]], {n, nn}]; Table[Count[Take[spfs, i], spfs[[i]]], {i, nn}]]; a246278 = NestList[Map[a003961, #] &, Table[2 k, {k, lim}], lim]; Table[a246278[[a055396@ n, a078898[[n]]]], {n, 2, lim}] (* Michael De Vlieger, Jan 04 2016, after Harvey P. Dale at A055396 and A078898 *) PROG (define (A249818 n) (if (= 1 n) n (A246278bi (A055396 n) (A078898 n)))) ;; Code for A246278bi given in A246278. ;; Alternatively: (define (A249818 n) (if (= 1 n) n (A246278bi (A055396 n) (A249822bi (A055396 n) (A246277 n))))) ;; Code for A249822bi given in A249822. CROSSREFS Inverse: A249817. There are three different "deep" versions of this permutation, recursing on values of A055396(n) and/or A078898(n), namely: A250246, A250248 and A250250. Other similar or related permutations: A249816. Cf. A000040, A005843, A020639, A055396, A078898, A083140, A083221, A246277, A246278, A246279, A249822. Differs from its inverse A249817 for the first time at n=33, where a(33) = 45, while A249817(33) = 39. Sequence in context: A250247 A250245 A250249 * A250248 A250246 A250250 Adjacent sequences:  A249815 A249816 A249817 * A249819 A249820 A249821 KEYWORD nonn AUTHOR Antti Karttunen, Nov 06 2014 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified November 13 10:29 EST 2019. Contains 329093 sequences. (Running on oeis4.)