A171602 Lesser of two consecutive primes such that half-sums are semiprimes.

3, 5, 7, 13, 19, 23, 31, 37, 67, 83, 89, 109, 127, 131, 199, 211, 251, 271, 307, 331, 379, 383, 389, 443, 449, 467, 487, 499, 509, 563, 661, 683, 719, 769, 797, 877, 929, 937, 971, 997, 1009, 1123, 1163, 1201, 1223, 1231, 1237, 1283, 1291, 1297, 1307, 1459

Offset

1,1

Links

Table of n, a(n) for n=1..52.

Example

(3+5)/2=4->2*2, (5+7)/2=6->2*3, (7+11)/2=9->3*3, (13+17)/2=15->3*5,..

Mathematica

f[n_]:=Last/@FactorInteger[n]=={1, 1}||Last/@FactorInteger[n]=={2}; lst={}; Do[p=Prime[n]; q=Prime[n+1]; s=(p+q)/2; If[f[s], AppendTo[lst, p]], {n, 6!}]; lst

Crossrefs

Sequence in context: A075579 A059788 A077171 * A155189 A065384 A354217

Adjacent sequences: A171599 A171600 A171601 * A171603 A171604 A171605

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Dec 12 2009

Status

approved