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Numbers m such that m mod k = 2 for only one integer k in 2..m.
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%I #26 Jun 02 2022 10:48:08

%S 5,6,7,9,13,15,19,21,25,31,33,39,43,45,49,55,61,63,69,73,75,81,85,91,

%T 99,103,105,109,111,115,129,133,139,141,151,153,159,165,169,175,181,

%U 183,193,195,199,201,213,225,229,231,235,241,243,253,259,265,271,273,279

%N Numbers m such that m mod k = 2 for only one integer k in 2..m.

%C From 7 on, sequence gives primes + two. This can be easily seen since the definition is equivalent to the following: "Numbers m such that there's only one k, 2 <= k <= m-2, that divides m-2." So k|(m-2) and values of k: m and m-1 are not considered since they don't divide m-2. But this 2nd statement is also the same as saying that m-2 is a prime number and so m = prime + 2.

%C Essentially the same as A048974. - _R. J. Mathar_, Jun 18 2008

%F a(n) = prime(n) + 2 = A000040(n) + 2 for n >= 3 (prime(3) = 5 > 4).

%t Join[{5,6},Prime[Range[3,60]]+2] (* _Harvey P. Dale_, Sep 05 2017 *)

%o (PARI) for(n=1,500,if(sum(k=2,n,if(n%k==2,1,0))==1,print1(n,", ")))

%o (Python)

%o from sympy import prime

%o a = lambda n : 5 if n==1 else (6 if n==2 else prime(n)+2)

%o # _Christoph B. Kassir_, Apr 14 2022

%Y Cf. A000040, A048974.

%K nonn

%O 1,1

%A Jared B. Ricks (jaredricks(AT)yahoo.com), Sep 24 2006

%E Edited by Herman Jamke (hermanjamke(AT)fastmail.fm), Sep 24 2006