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A249745
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Permutation of natural numbers: a(n) = (1 + A064989(A007310(n))) / 2.
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20
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1, 2, 3, 4, 6, 7, 9, 10, 5, 12, 15, 8, 16, 19, 21, 22, 13, 24, 11, 27, 30, 17, 31, 34, 36, 18, 37, 40, 20, 42, 28, 26, 45, 49, 51, 52, 54, 55, 29, 33, 25, 14, 57, 64, 43, 66, 69, 39, 35, 70, 75, 44, 76, 48, 79, 82, 61, 84, 23, 87, 90, 47, 46, 91, 96, 97, 99, 58, 56, 60, 100, 62, 73, 72, 106, 112, 114, 115, 65, 117, 120, 38, 94, 121
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OFFSET
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1,2
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LINKS
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FORMULA
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A007310(n) = A249735(a(n)) for all n >= 1. (This is the permutation which sorts the terms of A249735 into an ascending order, as they occur in A007310.)
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MATHEMATICA
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a249745[n_Integer] := Module[{f, p, a064989, a007310, a},
f[x_] := Transpose@FactorInteger[x];
p[x_] := Which[
x == 1, 1,
x == 2, 1,
True, NextPrime[x, -1]];
a064989[x_] := Times @@ Power[p /@ First[f[x]], Last[f[x]]];
a007310[x_] := Select[Range[x], MemberQ[{1, 5}, Mod[#, 6]] &];
a[x_] := (1 + a064989 /@ a007310[x])/2;
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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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