A072677 - OEIS

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A072677

a(n) = prime(prime(n)+1) where prime(k) is the k-th prime.

5, 7, 13, 19, 37, 43, 61, 71, 89, 113, 131, 163, 181, 193, 223, 251, 281, 293, 337, 359, 373, 409, 433, 463, 521, 557, 569, 593, 601, 619, 719, 743, 787, 809, 863, 881, 929, 971, 997, 1033, 1069, 1091, 1163, 1181, 1213, 1223, 1301, 1423, 1439, 1451, 1481, 1511, 1531, 1601, 1627, 1693, 1733, 1747, 1789, 1831, 1861, 1931

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OFFSET

1,1

COMMENTS

Prime numbers q for which the number of prime numbers smaller than q is also a prime number.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..10000

EXAMPLE

a(4)=prime(prime(4)+1), prime(4)=7, hence a(4)=prime(8)=19.

163 is in the sequence because (1) it is a prime number, (2) there are 37 prime numbers smaller than 163 and 37 is also a prime number.

MAPLE

with(numtheory): seq(ithprime(ithprime(i)+1), i=1..51);

MATHEMATICA

Prime[Prime[Range[60]]+1] (* Harvey P. Dale, Nov 07 2016 *)

PROG

(PARI) a(n) = prime(prime(n)+1); \\ Michel Marcus, Nov 17 2017

CROSSREFS

Cf. A000720, A006450, A055003, A072677.

Sequence in context: A264865 A293712 A297674 * A117249 A063910 A288632

Adjacent sequences: A072674 A072675 A072676 * A072678 A072679 A072680

KEYWORD

easy,nonn

AUTHOR

Mark Hudson (mrmarkhudson(AT)hotmail.com), Jul 05 2002

EXTENSIONS

Edited by N. J. A. Sloane, Nov 04 2018 at the suggestion of Georg Fischer, Nov 03 2018, merging a duplicate entry with this one.

STATUS

approved