A096870 Difference between the n-th repunit and the previous prime.

4, 2, 2, 18, 2, 20, 10, 2, 14, 52, 8, 18, 58, 58, 72, 4, 20, 74, 84, 58, 14, 18, 82, 168, 28, 50, 168, 84, 8, 138, 112, 82, 2, 28, 2, 62, 34, 50, 74, 24, 8, 54, 204, 22, 428, 40, 118, 200, 72, 40, 30, 42, 284, 44, 114, 268, 80, 18, 4, 74, 142, 182, 140, 112, 214, 152, 90

Offset

2,1

Links

Robert Israel, Table of n, a(n) for n = 2..1000

Formula

a(n) = A002275(n) - A096498(n) = A096499(n) - A096869(n).

Maple

f:= proc(n) local r; r:= (10^n-1)/9; r - prevprime(r) end proc:
map(f, [$2..100]); # Robert Israel, Feb 23 2017

Mathematica

PrevPrim[n_] := Block[{k = n - 1}, While[ !PrimeQ[k], k-- ]; k]; Table[(10^n - 1)/9 - PrevPrim[(10^n - 1)/9], {n, 2, 70}]
Table[With[{ru=(10^n-1)/9}, ru-NextPrime[ru, -1]], {n, 2, 70}] (* Harvey P. Dale, Aug 14 2011 *)

Crossrefs

Cf. A096869.

Sequence in context: A136202 A075418 A199221 * A350149 A350609 A261253

Adjacent sequences: A096867 A096868 A096869 * A096871 A096872 A096873

Keyword

nonn

Author

Robert G. Wilson v, Jul 12 2004

Status

approved