A033558 - OEIS

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A033558

a(n) = 2n - {smallest prime > n}.

0, 1, 1, 3, 3, 5, 3, 5, 7, 9, 9, 11, 9, 11, 13, 15, 15, 17, 15, 17, 19, 21, 17, 19, 21, 23, 25, 27, 27, 29, 25, 27, 29, 31, 33, 35, 33, 35, 37, 39, 39, 41, 39, 41, 43, 45, 41, 43, 45, 47, 49, 51, 47, 49, 51, 53, 55, 57

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,4

COMMENTS

By Bertrand's postulate, for n>3 a(n)>2. - Zak Seidov, Mar 06 2015

LINKS

Zak Seidov, Table of n, a(n) for n = 1..1000

Wikipedia, Bertrand's postulate

MAPLE

f := n->2*n-nextprime(n); [ seq(f(i), i=1..60) ];

MATHEMATICA

Table[2*n-NextPrime[n], {n, 60}] (* Harvey P. Dale, Jul 23 2018 *)