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A115307
a(n) = if n<7 then n else 7*a(floor(n/7)) + 6 - n mod 7.
9
1, 2, 3, 4, 5, 6, 13, 12, 11, 10, 9, 8, 7, 20, 19, 18, 17, 16, 15, 14, 27, 26, 25, 24, 23, 22, 21, 34, 33, 32, 31, 30, 29, 28, 41, 40, 39, 38, 37, 36, 35, 48, 47, 46, 45, 44, 43, 42, 97, 96, 95, 94, 93, 92, 91, 90, 89, 88, 87, 86, 85, 84, 83, 82, 81, 80, 79, 78, 77, 76, 75, 74
OFFSET
1,2
COMMENTS
Self-inverse permutation of the natural numbers;
A115310(n+5,6) = a(n);
if n is written in base 7 representation, then a(n) is the value after replacing all digits d (but not the leading one) by 6-d.
KEYWORD
nonn,base
AUTHOR
Reinhard Zumkeller, Jan 20 2006
STATUS
approved