A060230 - OEIS

%I #14 Jan 29 2018 23:28:01

%S 419,1049,2309,2729,3359,5879,6089,6299,7349,7559,8819,9239,10499,

%T 10709,11549,11969,15329,18059,21839,25409,26249,26879,28349,29399,

%U 30869,31079,32969,33179,33599,33809,34649,35279,37589,40529,42839

%N Smaller of twin primes whose middle term is a multiple of A002110(4)=210.

%C Number of terms less than 10^k: 0, 0, 0, 1, 12, 80, 542, 3908, 29229, ... - _Muniru A Asiru_, Jan 29 2018

%H Harvey P. Dale, <a href="/A060230/b060230.txt">Table of n, a(n) for n = 1..1000</a>

%e For the pair {1049,1051} (1049+1051)/2 = 5*210.

%p select(n->isprime(n) and isprime(n+2), [seq(210*k - 1, k=1..10^3)]); # _Muniru A Asiru_, Jan 29 2018

%t Select[210*Range[250],And@@PrimeQ[#+{1,-1}]&]-1 (* _Harvey P. Dale_, Aug 25 2013 *)

%o (GAP) P:=Filtered([1..10^7], IsPrime);;

%o P1:=List(Filtered(Filtered(List([1..Length(P)-1], n -> [P[n],P[n+1]]), i -> i[2]-i[1]=2), j -> (j[1]+j[2]) mod 210 = 0), k -> k[1]); # _Muniru A Asiru_, Jan 29 2018

%o (PARI) is(n)=(n+1)%210==0 && isprime(n+2) && isprime(n) \\ _Charles R Greathouse IV_, Jan 29 2018

%Y A001359, A002110, A060229, A060231.

%K nonn

%O 1,1

%A _Labos Elemer_, Mar 21 2001

%E Minor edits by _Ray Chandler_, Apr 02 2009