A097457 If n is prime replace with the n-th nonprime otherwise replace with the n-th prime.

2, 4, 6, 7, 9, 13, 12, 19, 23, 29, 18, 37, 21, 43, 47, 53, 26, 61, 28, 71, 73, 79, 34, 89, 97, 101, 103, 107, 42, 113, 45, 131, 137, 139, 149, 151, 52, 163, 167, 173, 57, 181, 60, 193, 197, 199, 65, 223, 227, 229, 233, 239, 74, 251, 257, 263, 269, 271, 81, 281, 84, 293

Offset: 1

Author

Cino Hilliard, Aug 23 2004

Keywords

• nonn

Examples

			4 is composite so replace it with prime(4) = 7, the 4th entry in the table.
		

Crossrefs

Cf. A026234.

Programs

PARI

flipcomppr(n) = { for(x=1,n, if(isprime(x),y=composite(x),y=prime(x)); print1(y",") ) } /* the n-th composite */ composite(n) = { local(c,x); c=1; x=0; while(c <= n, x++; if(!isprime(x),c++); ); return(x) } /* Note: for more efficient code, see A018252 */

PARI

A097457 = n->if(isprime(n),A018252(n),prime(n)) \\ M. F. Hasler, Jan 29 2014

Extensions

Definition and offset corrected by M. F. Hasler, Jan 29 2014