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A353653
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Unique monotonic sequence of positive integers satisfying a(a(n)) = k*(n-1) + 3, where k = 6.
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3
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2, 3, 9, 10, 11, 12, 13, 14, 15, 21, 27, 33, 39, 45, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 93, 99, 105, 111, 117, 123, 129, 135, 141, 147, 153, 159, 165
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OFFSET
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1,1
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COMMENTS
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Numbers m such that the base-6 representation of (5*m-3) starts with 11 or 12 or 13 or 14 or 15 or ends with 0.
First differences give a run of 6^i 1's followed by a run of 6^i 6's, for i >= 0.
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LINKS
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FORMULA
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For n in the range (2*6^i + 3)/5 <= n < (7*6^i + 3)/5, for i >= 0:
a(n) = n + 6^i.
a(n+1) = 1 + a(n).
Otherwise, for n in the range (7*6^i + 3)/5 <= n < (12*6^i + 3)/5, for i >= 0:
a(n) = 6*(n - 6^i) - 3.
a(n+1) = 6 + a(n).
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EXAMPLE
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a(5) = 11 because (2*6^1 + 3)/3 <= 5 < (7*6^1 + 3)/5, hence a(5) = 5 + 6^1 = 11;
a(10) = 21 because (7*6^1 + 3)/5 <= 10 < (12*6^1 + 3)/5, hence a(10) = 6*(10 - 6^1) - 3 = 21.
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MATHEMATICA
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okQ[m_] := With[{id = IntegerDigits[5 m - 3, 6] }, MatchQ[id[[1 ;; 2]], {1, 1}|{1, 2}|{1, 3}|{1, 4}|{1, 5}] || id[[-1]] == 0];
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PROG
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(C++)
/* program used to generate the b-file */
#include<iostream>
using namespace std;
int main(){
int cnt1=1, flag=0, cnt2=1, a=2;
for(int n=1; n<=10000; n++) {
cout<<n<<" "<<a<<endl;
if(cnt2==cnt1) {
flag=1-flag;
cnt1=1;
if(flag) a+=1;
else {
a+=6;
cnt2*=6;
}
}
else {
cnt1++;
a+=(flag?6:1);
}
}
return 0;
}
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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