1,2

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

a(1)=1 because 3*prime(1)-4=2 is prime and 3*prime(1)+4=10 is composite; a(2)=4 because 3*prime(4)-4=17 is prime and 3*prime(4)+4=25 is composite.

Select[Range[200], Total[Boole[PrimeQ[3Prime[#]+{4, -4}]]]==1&] (* Harvey P. Dale, May 08 2019 *)

Sequence in context: A179242 A104425 A345447 * A080746 A246362 A069909

Adjacent sequences: A174255 A174256 A174257 * A174259 A174260 A174261

nonn,easy

Juri-Stepan Gerasimov, Mar 14 2010

Corrected by Charles R Greathouse IV, Mar 19 2010

approved