A280030 a(1)=5; thereafter, if n odd, a(n) = a(n-1)-st prime, and if n even, a(n) = a(n-1)-st nonprime.

5, 9, 23, 34, 139, 180, 1069, 1274, 10399, 11815, 125933, 138847, 1854341, 2003514, 32513171, 34639222, 667169599, 703599332, 15783876803, 16518738034, 425079924023, 442239042120, 12891534052099, 13348915604303, 436194466471661

Offset

1,1

Comments

This is the sequence S_3 mentioned in A141436. The primes and nonprimes alternate.

Links

Table of n, a(n) for n=1..25.

Maple

# See A280028 for Maple program

Mathematica

nonPrime[n_Integer] := FixedPoint[n + PrimePi@# &, n + PrimePi@n]; a[n_] := If[OddQ@ n, Prime@ a[n -1], nonPrime[ a[n -1]]]; a[1] = 5; Array[a, 24] (* Robert G. Wilson v, Dec 28 2016 *)

Crossrefs

Cf. A000040, A018252, A141436, A280028, A280029.

Sequence in context: A343803 A194802 A229925 * A074340 A079993 A163607

Adjacent sequences: A280027 A280028 A280029 * A280031 A280032 A280033

Keyword

nonn

Author

N. J. A. Sloane, Dec 25 2016

Extensions

a(12)-a(23) from Chai Wah Wu, Dec 25 2016

a(24) from Hans Havermann, Dec 25 2016

a(25) from Chai Wah Wu, Dec 26 2016

Status

approved