A104297 a(n) = prime((a(n-1) + 1)/2), a(1) = 21.

21, 31, 53, 103, 239, 659, 2213, 8887, 42473, 240151, 1584607, 12069311, 105036509, 1034651039, 11438277847, 140842283467, 1918464961643, 28731994949989, 470518379103089, 8383514543462161, 161792182891599881, 3368158595757642587

Offset

1,1

Links

Table of n, a(n) for n=1..22.

Mathematica

a[1] = 21; a[n_] := a[n] = Prime[(a[n - 1] + 1)/2]; Table[ a[n], {n, 18}] (* Robert G. Wilson v, Mar 24 2005 *)

Crossrefs

Cf. A104296, A104298, A116457.

Sequence in context: A113762 A032585 A138822 * A138600 A106324 A208293

Adjacent sequences: A104294 A104295 A104296 * A104298 A104299 A104300

Keyword

nonn,more

Author

Zak Seidov, Mar 20 2005

Extensions

a(14)-a(18) from Robert G. Wilson v, Mar 24 2005

a(16)-a(18) corrected and a(19)-a(22) added by Amiram Eldar, Jul 15 2025

Status

approved