cp's OEIS Frontend

A269844 Primes equal to the sum of a pair of consecutive integers which are both squarefree.

%I A269844 #36 Oct 26 2021 02:14:48
%S A269844 5,11,13,29,43,59,61,67,83,131,139,157,173,211,227,229,277,283,317,
%T A269844 331,347,373,389,419,421,443,461,509,547,563,571,619,643,653,659,661,
%U A269844 691,709,733,787,797,821,853,859,877,907,941,947,997,1019,1021,1069,1091,1093,1109,1123,1163,1181,1213
%N A269844 Primes equal to the sum of a pair of consecutive integers which are both squarefree.
%C A269844 The associated prime factors will always include 2 and 3.
%C A269844 Will every prime number be encountered as a prime factor from the sequence entries?
%C A269844 The sequence appears to share many of it terms with A001122.
%C A269844 What is the asymptotic behavior?
%C A269844 Conjecture: sequence has density A271780/2 = A005597*4/Pi^2 = 0.2675535... in the primes. - _Charles R Greathouse IV_, Jan 24 2018
%C A269844 The prime terms of A179017 (except 3). - _Bill McEachen_, Oct 21 2021
%H A269844 Charles R Greathouse IV, <a href="/A269844/b269844.txt">Table of n, a(n) for n = 1..10000</a>
%H A269844 Bill McEachen, <a href="/A269844/a269844.png">A269844_vs_A001122</a>
%e A269844 277 = 138 + 139 = 2*3*23 + 139 is in the sequence since both terms are squarefree.
%e A269844 281 = 140 + 141 = 2^2*5*7 + 3*47 is not in the sequence since the former term is divisible by 2^2.
%t A269844 Select[Prime@ Range[3, 200], PrimeOmega@ # == PrimeNu@ # &[# (# + 1)] &@ Floor[#/2] &] (* _Michael De Vlieger_, Mar 07 2016 *)
%o A269844 (PARI)
%o A269844 genit(maxx)={for(i5=3,maxx,n=prime(i5);a=factor(floor(n/2.));b=factor(ceil(n/2.));clear=1;for(j5=1,omega(floor(n/2.)),if(a[j5,2]<>1,clear=0));
%o A269844 for(j7=1,omega(ceil(n/2.)),if(b[j7,2]<>1,clear=0));if(clear>0,print1(n,",")));}
%o A269844 (PARI) is(n)=isprime(n) && issquarefree(n\2) && issquarefree(n\2+1) \\ _Charles R Greathouse IV_, Jan 24 2018
%o A269844 (PARI) list(lim)=my(v=List(),t=1); forfactored(k=3,(lim+1)\2, if(vecmax(k[2][,2])>1, t=0, ; if(t && isprime(t=2*k[1]-1), listput(v,t)); t=1)); Vec(v) \\ _Charles R Greathouse IV_, Jan 24 2018
%Y A269844 Cf. A001122 (primes with primitive root 2), A179017.
%Y A269844 Cf. A005597, A271780.
%K A269844 nonn,easy
%O A269844 1,1
%A A269844 _Bill McEachen_, Mar 06 2016