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A235041
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Factorization-preserving bijection from nonnegative integers to GF(2)[X]-polynomials, version which fixes the elements that are irreducible in both semirings.
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14
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0, 1, 2, 3, 4, 25, 6, 7, 8, 5, 50, 11, 12, 13, 14, 43, 16, 55, 10, 19, 100, 9, 22, 87, 24, 321, 26, 15, 28, 91, 86, 31, 32, 29, 110, 79, 20, 37, 38, 23, 200, 41, 18, 115, 44, 125, 174, 47, 48, 21, 642, 89, 52, 117, 30, 227, 56, 53, 182, 59, 172, 61, 62, 27, 64
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OFFSET
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0,3
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COMMENTS
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Like A091202 this is a factorization-preserving isomorphism from integers to GF(2)[X]-polynomials. The latter are encoded in the binary representation of n like this: n=11, '1011' in binary, stands for polynomial x^3+x+1, n=25, '11001' in binary, stands for polynomial x^4+x^3+1. However, this version does not map the primes (A000040) straight to the irreducible GF(2)[X] polynomials (A014580), but instead fixes the intersection of those two sets (A091206), and maps the elements in their set-wise difference A000040 \ A014580 (= A091209) in numerical order to the set-wise difference A014580 \ A000040 (= A091214).
The composite values are defined by the multiplicativity. E.g., we have a(3n) = A048724(a(n)) and a(3^n) = A001317(n) for all n.
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LINKS
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FORMULA
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a(0)=0, a(1)=1, a(p) = p for those primes p whose binary representations encode also irreducible GF(2)[X]-polynomials (i.e., p is in A091206), and for the rest of the primes q (those whose binary representation encode composite GF(2)[X]-polynomials, i.e., q is in A091209), a(q) = A091214(A235043(q)), and for composite natural numbers, a(p * q * r * ...) = a(p) X a(q) X a(r) X ..., where p, q, r, ... are primes and X stands for the carryless multiplication (A048720) of GF(2)[X] polynomials encoded as explained in the Comments section.
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EXAMPLE
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a(2)=2, a(3)=3 and a(7)=7, as 2, 3 and 7 are all in A091206.
a(4) = a(2*2) = a(2) X a(2) = 2 X 2 = 4.
a(9) = a(3*3) = a(3) X a(3) = 3 X 3 = 5.
a(5) = 25, as 5 is the first term of A091209 and 25 is the first term of A091214.
a(10) = a(2*5) = a(2) X a(5) = 2 X 25 = 50.
Similarly, a(17) = 55, as 17 is the second term of A091209 and 55 is the second term of A091214.
a(21) = a(3*7) = a(3) X a(7) = 3 X 7 = 9.
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PROG
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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