A241082 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.

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

Offset

1,2

Links

Table of n, a(n) for n=1..66.

Example

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.

Prog

(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

Crossrefs

Sequence in context: A087572 A085107 A358242 * A219789 A034694 A050921

Adjacent sequences: A241079 A241080 A241081 * A241083 A241084 A241085

Keyword

nonn

Author

J. Lowell, Apr 15 2014

Extensions

More terms from Michel Marcus, Apr 27 2014

Status

approved