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Search: id:A091089
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| A091089 |
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Numbers which form a prime by appending a 3-digit odd number and form no primes by appending any 1- or 2-digit odd number. |
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4
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| 16557, 16718, 26378, 35921, 46524, 46867, 50018, 55187, 58374, 58452, 60850, 63714, 68771, 71299, 78035, 78269, 81661, 84213, 89052, 90157, 95490, 97080, 102892, 105690, 108682, 115558, 115994, 116138, 116305, 121097, 128192, 131194
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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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. 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
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a(1)=16557 because 16557 is first number which which requires a 3-digit odd number be appended to it to form a prime. 165571, 165573, 165575, ..., 165579, 1655711, 1655713, ..., 1655799 are all nonprime numbers. 16557103 is the first prime formed by appending odd numbers to 16657. a(2) = 16718 because 16718111 is the first prime formed by appending odd numbers to 16718.
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CROSSREFS
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Cf. A032352 (a(n) requires at least a 2-digit odd number), A068695 (minimum odd number that must be appended to n to form a prime).
Sequence in context: A031829 A057680 A157796 this_sequence A109028 A057329 A108843
Adjacent sequences: A091086 A091087 A091088 this_sequence A091090 A091091 A091092
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KEYWORD
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base,nonn
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AUTHOR
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Chuck Seggelin (barkeep(AT)plastereddragon.com), Dec 18 2003
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