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A091088
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a(n) = the minimum odd number that must be appended to n to form a prime.
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0
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3, 1, 3, 1, 1, 3, 1, 1, 3, 7, 1, 3, 7, 1, 9, 1, 3, 3, 1, 1, 11, 1, 3, 3, 1, 1, 3, 1, 1, 3, 7, 1, 17, 1, 7, 3, 7, 3, 3, 7, 1, 9, 1, 1, 3, 7, 1, 9, 7, 1, 3, 13, 1, 23, 1, 7, 3, 1, 7, 3, 1, 3, 11, 1, 1, 3, 1, 3, 3, 1, 1, 9, 7, 3, 3, 1, 1, 3, 7, 7, 9, 1, 1, 9, 19, 3, 3, 7, 1, 23, 7, 1, 9, 7, 1, 3, 7, 1, 3, 1, 9, 3
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| Many numbers become prime by appending a one-digit odd number. Some numbers (such as 20, 32, 51, etc.) require a 2 digit odd number (A032352 has these). In the first 100,000 values of n there are only 22 that require a 3 digit odd number (A091089). There probably are some values that require odd numbers of 4 or more digits, but these are likely to be very large.
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EXAMPLE
| a(0)=3 because 3 is the minimum odd number which when appended to 0 forms a prime (03 = 3 = prime). a(20)=11 because 11 is the minimum odd number which when appended to 20 forms a prime (201, 203, 205, 207, 209 are all nonprime, 2011 is prime).
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CROSSREFS
| Essentially the same as A068695, which is the main entry for this sequence.
Cf. A032352 (a(n) requires at least a 2 digit odd number) A091089 (a(n) requires at least a 3 digit odd number).
Sequence in context: A100375 A066975 A098877 * A115627 A128218 A010283
Adjacent sequences: A091085 A091086 A091087 * A091089 A091090 A091091
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KEYWORD
| base,easy,nonn
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AUTHOR
| Chuck Seggelin (barkeep(AT)plastereddragon.com), Dec 18 2003
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