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A241082
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a(n) = n for 1 and prime numbers. For composite numbers, first prime term in sequence starting with n and each time adding smallest prime number not a divisor of the preceding term.
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0
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1, 2, 3, 7, 5, 11, 7, 11, 11, 13, 11, 17, 13, 17, 17, 19, 17, 23, 19, 23, 23, 29, 23, 29, 29, 29, 29, 31, 29, 37, 31, 37, 37, 37, 37, 41, 37, 41, 41, 43, 41, 47, 43, 47, 47, 53, 47, 53, 53, 53, 53, 59, 53, 59, 59, 59, 59, 61, 59, 67, 61, 67, 67, 67, 67, 71
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OFFSET
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1,2
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LINKS
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EXAMPLE
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a(22) = 29 because the smallest prime number not a divisor of 22 is 3, and 22+3=25, and 25 is composite, and the smallest prime number not a divisor of 25 is 2, and 25+2=27, and 27 is composite, and the smallest prime number not a divisor of 27 is 2, and 27+2=29, a prime number.
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PROG
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(PARI) a(n) = {if ((n==1) || isprime(n), return(n)); k = n; while (! isprime(k), p = 2; while (! (k % p), p = nextprime(p+1)); k += p; ); k; } \\ Michel Marcus, Apr 27 2014
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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