A104293 a(n) = prime((prime(n)-1)/2).

2, 3, 5, 11, 13, 19, 23, 31, 43, 47, 61, 71, 73, 83, 101, 109, 113, 137, 149, 151, 167, 179, 193, 223, 229, 233, 241, 251, 263, 307, 313, 337, 347, 373, 379, 397, 419, 431, 443, 461, 463, 499, 503, 521, 523, 571, 607, 617, 619

Offset

2,1

Comments

n=1 is a degenerate case because prime(1)=2, (prime(n)-1)/2 = 1/2 and there is no prime(1/2).

Links

Table of n, a(n) for n=2..50.

Formula

a(n) = A104294(n) - A104295(n).

a(n) = prime(A005097(n)). - Michel Marcus, Mar 29 2015

Example

a(5)=11 because prime((prime(5)-1)/2) = prime((11-1)/2) = prime(5) = 11;
a(7)=19 because prime((prime(7)-1)/2) = prime((17-1)/2) = prime(8) = 19.

Maple

seq(ithprime((ithprime(i)-1)/2), i=2..100); # Robert Israel, Mar 29 2015

Mathematica

Table[Prime[(Prime[n]-1)/2], {n, 2, 50}]

Prog

(PARI) vector(100, n, prime((prime(n+1)-1)/2)) \\ Derek Orr, Mar 29 2015

Crossrefs

Cf. A104294 (prime((prime(n)+1)/2)), A104295.

Sequence in context: A153135 A038615 A280930 * A153002 A042999 A089194

Adjacent sequences: A104290 A104291 A104292 * A104294 A104295 A104296

Keyword

easy,nonn

Author

Zak Seidov, Feb 28 2005

Status

approved