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A165634
Start with x=1 and repeat: if x is a prime number then (append i and then x, with x=prime(i)) else (only append x), continue with x:=x+1.
3
1, 1, 2, 2, 3, 4, 3, 5, 6, 4, 7, 8, 9, 10, 5, 11, 12, 6, 13, 14, 15, 16, 7, 17, 18, 8, 19, 20, 21, 22, 9, 23, 24, 25, 26, 27, 28, 10, 29, 30, 11, 31, 32, 33, 34, 35, 36, 12, 37, 38, 39, 40, 13, 41, 42, 14, 43, 44, 45, 46, 15, 47, 48, 49, 50, 51, 52, 16, 53, 54, 55, 56, 57, 58, 17, 59
OFFSET
1,3
COMMENTS
All positive integers occur exactly twice: A095117 and A095116 give positions of first and second occurrences.
LINKS
EXAMPLE
1,(1,2),(2,3),4,(3,5),6,(4,7),8,9,10,(5,11),12, ... .
PROG
(Haskell)
a165634 n = a165634_list !! (fromInteger n - 1)
a165634_list = concatMap (\x ->
if a010051 x == 1 then [a049084 x, x] else [x]) [1..]
-- Reinhard Zumkeller, Apr 17 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Sep 23 2009
STATUS
approved