A167397 - OEIS

%I #7 Feb 18 2019 10:43:23

%S 1,21,34,43,48,61,72,75,80,87,102,115,118,143,148,151,156,193,204,213,

%T 230,235,240,253,268,281,290,303,308,323,328,335,340,345,348,353,360,

%U 363,370,399,402,407,414,423,434,441,444,451,454,459,490,495,504,509

%N n-th single (or isolated or non-twin) prime minus n.

%F a(n) = A007510(n)  -A000027(n).

%e a(1) =  2 - 1 =  1,

%e a(2) = 23 - 2 = 21,

%e a(3) = 37 - 3 = 34.

%p A007510 := proc(n) option remember; if n <= 2 then op(n,[2,23]) ; else for a from procname(n-1)+2 by 2 do if isprime(a) and not isprime(a+2) and not isprime(a-2) then return a; end if; end do: end if; end proc:

%p A167397 := proc(n) A007510(n)-n ; end proc:

%p seq(A167397(n),n=1..120) ; # _R. J. Mathar_, May 30 2010

%Y Cf. A000027, A007510.

%K nonn

%O 1,2

%A _Juri-Stepan Gerasimov_, Nov 02 2009, Nov 05 2009

%E Corrected (220 replaced with 230, 225 with 235) by _R. J. Mathar_, May 30 2010