OFFSET
1,1
COMMENTS
A permutation of the positive integers. - M. F. Hasler, Jan 29 2014
LINKS
Zak Seidov, Table of n, a(n) for n = 1..1000.
FORMULA
EXAMPLE
a(1) = 2 because 1 is not prime and the first prime is 2.
a(2) = 1 because 2 is prime and the first nonprime is 1.
a(3) = 4 because 3 is prime and the second nonprime is 4.
a(4) = 3 because 4 is not prime and the second prime is 3.
a(5) = 6 because 5 is prime and the third nonprime is 6.
MATHEMATICA
nonPrimePi[n_] := n - PrimePi[n]; nonPrime[n_] := FixedPoint[n + PrimePi[#] &, n + PrimePi[n]]; A026234[n_] := If[PrimeQ[n], nonPrime[PrimePi[n]], Prime[nonPrimePi[n]]]; Table[A026234[n], {n, 200}] (* Enrique Pérez Herrero, Jan 28 2014 *)
PROG
(PARI) c=p=0; vector(99, n, if(isprime(n), while(isprime(c++), ); c, prime(p++))) \\ M. F. Hasler, Jan 29 2014
(PARI) A026234 = n->if(isprime(n), A018252(primepi(n)), prime(n-primepi(n))) \\ M. F. Hasler, Jan 29 2014
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved