A089965 Both n + 1 and n/2 + 1 are primes.

2, 4, 12, 36, 60, 72, 156, 192, 276, 312, 396, 420, 456, 540, 612, 660, 672, 732, 756, 876, 996, 1092, 1152, 1200, 1212, 1236, 1320, 1380, 1452, 1620, 1656, 1752, 1872, 1932, 1992, 2016, 2136, 2340, 2472, 2556, 2592, 2796, 2856, 2916, 3060, 3216, 3252

Offset: 1

Author

Joseph L. Pe, Jan 18 2004

Keywords

• nonn

Crossrefs

Cf. A005383.

Programs

Mathematica

Select[Range[5*10^3], PrimeQ[ # + 1] && PrimeQ[ #/2 + 1] &]

Formula

a(n) = A005383(n)-1. - Robert Israel, Dec 13 2018