A023515 a(n) = prime(n)*prime(n-1) - 1.

1, 5, 14, 34, 76, 142, 220, 322, 436, 666, 898, 1146, 1516, 1762, 2020, 2490, 3126, 3598, 4086, 4756, 5182, 5766, 6556, 7386, 8632, 9796, 10402, 11020, 11662, 12316, 14350, 16636, 17946, 19042, 20710, 22498, 23706, 25590, 27220, 28890

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

Comments

a(1) = 1 assumes the not generally accepted convention prime(0) = 1. - Klaus Brockhaus, Dec 23 2010

Links

• Muniru A Asiru, Table of n, a(n) for n = 1..5000

Crossrefs

Cf. A120875 (a subsequence).

Programs

Magma

[ NthPrime(n-1)*NthPrime(n)-1: n in [1..50] ]; // Vincenzo Librandi, Dec 23 2010; simplified by Klaus Brockhaus, Dec 23 2010

Maple

1,seq(ithprime(n)*ithprime(n-1)-1,n=2..40); # Muniru A Asiru, Apr 27 2019

Mathematica

Prepend[Table[Prime@ n Prime[n - 1] - 1, {n, 2, 12}], 1] (* Michael De Vlieger, Nov 10 2015 *)
Join[{1},Times@@#-1&/@Partition[Prime[Range[40]],2,1]] (* Harvey P. Dale, Jul 06 2024 *)

PARI

a(n) = if(n==1, 1, prime(n)*prime(n-1)-1) \\ Altug Alkan, Nov 10 2015

Formula

From Jason Kimberley, Oct 23 2015: (Start)

a(n) = A006094(n-1) - 1 = A000040(n-1)*A000040(n)-1, for n>1.

a(n) = 2*A102770(n-2), for n>2.

(End)