A175218 The third nonprimes after the primes.

8, 8, 9, 10, 15, 16, 21, 22, 26, 33, 34, 40, 45, 46, 50, 56, 63, 64, 70, 75, 76, 82, 86, 92, 100, 105, 106, 111, 112, 116, 130, 134, 141, 142, 153, 154, 160, 166, 170, 176, 183, 184, 195, 196, 201, 202, 214, 226, 231, 232, 236, 243, 244, 254, 260, 266, 273, 274

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Formula

For n>2: a(n) = A000040(n) + 2 + A010051(A000040(n) + 2) + 1. - Reinhard Zumkeller, Mar 29 2010 [corrected by Georg Fischer, Oct 06 2024]

Example

prime(49) = 227, prime(50) = 229, therefore (228=1st, 230=2nd nonprime), 231 = a(49). - Georg Fischer, Oct 06 2024

Mathematica

tnp[p_]:=Select[Range[p+1, p+6], CompositeQ][[3]]; Table[tnp[p], {p, Prime[Range[60]]}] (* Harvey P. Dale, Dec 28 2025 *)

Prog

(PARI) a(n) = if(n<=2, 8, prime(n) + 2 + isprime(prime(n)+2) + 1) /* Georg Fischer, Oct 06 2024 */

Crossrefs

Cf. A175216, A175217, A175219, A175220.

Sequence in context: A187107 A179412 A298186 * A298916 A329032 A001732

Adjacent sequences: A175215 A175216 A175217 * A175219 A175220 A175221

Keyword

nonn

Author

Jaroslav Krizek, Mar 06 2010

Extensions

More terms from Reinhard Zumkeller, Mar 29 2010

a(49), a(52) and a(57) corrected by Georg Fischer, Oct 06 2024

Status

approved