A115396 Smallest prime p such that p +- 2*n are semiprimes.

23, 29, 71, 17, 59, 37, 71, 41, 67, 29, 43, 109, 59, 37, 173, 53, 43, 151, 47, 79, 127, 79, 97, 73, 71, 67, 79, 89, 83, 109, 71, 79, 151, 101, 139, 97, 109, 101, 127, 89, 103, 239, 101, 97, 211, 113, 109, 151, 107, 109, 151, 113, 131, 157, 149, 137, 139, 131

Offset

1,1

Links

Table of n, a(n) for n=1..58.

Example

a(100)=251 because 251-2*100=51=7*17 (semiprime), 251+2*100=451=11*41 (semiprime) [corrected by Sean A. Irvine, Nov 18 2025].

Mathematica

sp[n_]:=Module[{p=NextPrime[2n]}, While[PrimeOmega[p+2n]!=2||PrimeOmega[p-2n]!=2, p=NextPrime[p]]; p]; Array[sp, 60] (* Harvey P. Dale, Nov 19 2025 *)

Crossrefs

Cf. A063643, A117328.

Sequence in context: A092518 A355983 A110584 * A180538 A227217 A229176

Adjacent sequences: A115393 A115394 A115395 * A115397 A115398 A115399

Keyword

nonn

Author

Zak Seidov, Mar 08 2006

Extensions

Corrected by Sean A. Irvine and Harvey P. Dale, Nov 18 2025

Status

approved