A165972 - OEIS

%I #6 Oct 01 2015 10:51:52

%S 1,4,6,10,12,16,18,22,28,30,36,40,42,46,52,58,60,66,70,72,78,82,88,96,

%T 100,102,106,108,112,126,130,136,138,148,150,156,162,166,172,178,180,

%U 190,192,196,198,210,222,226,228,232,238,240,250,256,262,268,270,276

%N Nonprimes k such that the sum of the smallest and largest divisor of k is prime.

%C n-(-1)^n is prime.

%C Largest nonprime<prime(n+1) or largest nonprime<n-th odd prime. [From _Juri-Stepan Gerasimov_, Oct 29 2009]

%F A006093 \ {2}.

%e k=1 is in the sequence because 1+1=2 is prime. k=4 is in the sequence because 1+4=5 is prime.

%t Select[Range[300],!PrimeQ[#]&&With[{d=Divisors[#]},PrimeQ[d[[1]]+ d[[-1]]]]&] (* _Harvey P. Dale_, Oct 01 2015 *)

%Y Cf. A000040, A006093, A018252.

%K nonn,less

%O 1,2

%A _Juri-Stepan Gerasimov_, Oct 02 2009, Oct 14 2009

%E Entries checked by _R. J. Mathar_, Oct 10 2009