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 A245703 Permutation of natural numbers: a(1) = 1, a(p_n) = A014580(a(n)), a(c_n) = A091242(a(n)), where p_n = n-th prime, c_n = n-th composite number and A014580(n) and A091242(n) are binary codes for n-th irreducible and n-th reducible polynomials over GF(2), respectively. 19
 1, 2, 3, 4, 7, 5, 11, 6, 8, 12, 25, 9, 13, 17, 10, 14, 47, 18, 19, 34, 15, 20, 31, 24, 16, 21, 62, 26, 55, 27, 137, 45, 22, 28, 42, 33, 37, 23, 29, 79, 59, 35, 87, 71, 36, 166, 41, 58, 30, 38, 54, 44, 61, 49, 32, 39, 99, 76, 319, 46, 91, 108, 89, 48, 200, 53, 97, 75, 40, 50, 203, 70, 67, 57, 78, 64, 43, 51 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS All the permutations A091202, A091204, A106442, A106444, A106446, A235041 share the same property that primes (A000040) are mapped bijectively to the binary representations of irreducible GF(2) polynomials (A014580) but while they determine the mapping of composites (A002808) to the corresponding binary codes of reducible polynomials (A091242) by a simple multiplicative rule, this permutation employs index-recursion also in that case. LINKS Antti Karttunen, Table of n, a(n) for n = 1..10001 FORMULA a(1) = 1, a(p_n) = A014580(a(n)) and a(c_n) = A091242(a(n)), where p_n is the n-th prime, A000040(n) and c_n is the n-th composite, A002808(n). a(1) = 1, after which, if A010051(n) is 1 [i.e. n is prime], then a(n) = A014580(a(A000720(n))), otherwise a(n) = A091242(a(A065855(n))). As a composition of related permutations: a(n) = A245702(A135141(n)). a(n) = A091204(A245821(n)). Other identities. For all n >= 1, the following holds: a(A007097(n)) = A091230(n). [Maps iterates of primes to the iterates of A014580. Permutation A091204 has the same property] A091225(a(n)) = A010051(n). [Maps primes to binary representations of irreducible GF(2) polynomials, A014580, and nonprimes to union of {1} and the binary representations of corresponding reducible polynomials, A091242. The permutations A091202, A091204, A106442, A106444, A106446 and A235041 have the same property.] PROG (PARI) allocatemem(123456789); a014580 = vector(2^18); a091242 = vector(2^22); isA014580(n)=polisirreducible(Pol(binary(n))*Mod(1, 2)); \\ This function from Charles R Greathouse IV i=0; j=0; n=2; while((n < 2^22), if(isA014580(n), i++; a014580[i] = n, j++; a091242[j] = n); n++) A245703(n) = if(1==n, 1, if(isprime(n), a014580[A245703(primepi(n))], a091242[A245703(n-primepi(n)-1)])); for(n=1, 10001, write("b245703.txt", n, " ", A245703(n))); (Scheme, with memoization-macro definec) (definec (A245703 n) (cond ((= 1 n) n) ((= 1 (A010051 n)) (A014580 (A245703 (A000720 n)))) (else (A091242 (A245703 (A065855 n)))))) CROSSREFS Inverse: A245704. Cf. A000040, A002808, A000720, A007097, A010051, A014580, A065855, A091225, A091230, A091242. Similar or related permutations: A091202, A091204, A106442, A106444, A106446, A235041, A135141, A245701, A245702, A245821, A245822, A244987, A245450. Sequence in context: A191438 A191730 A233560 * A260426 A167151 A273014 Adjacent sequences:  A245700 A245701 A245702 * A245704 A245705 A245706 KEYWORD nonn,look AUTHOR Antti Karttunen, Aug 02 2014 STATUS approved

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Last modified February 23 18:13 EST 2019. Contains 320437 sequences. (Running on oeis4.)