cp's OEIS Frontend

A338262 Primes p such that the area of the triangle with sides p and the next two primes achieves a record for closeness to a prime.

%I A338262 #27 Oct 24 2020 04:14:30
%S A338262 2,3,5,239,2521,12239,121421,869657,23638231,30656909,47964149,
%T A338262 48203291,57273361,552014783,754751369,941234383
%N A338262 Primes p such that the area of the triangle with sides p and the next two primes achieves a record for closeness to a prime.
%e A338262 a(3)=5 is in the sequence because 5 is a prime, the triangle with sides 5, 7, 11 has area 3*sqrt(299)/4 whose distance to the nearest prime, 13, is approximately 0.0313, and this is less than any distance previously achieved.
%p A338262 atr:= proc(p,q,r) local s; s:= (p+q+r)/2; sqrt(s*(s-p)*(s-q)*(s-r)) end proc:
%p A338262 R:= 2,3: p:= 3: q:= 5: r:= 7: count:= 2: dmin:= 7 - atr(3,5,7):
%p A338262 while count < 8 do
%p A338262 p:= q: q:= r: r:= nextprime(r);
%p A338262 a:= atr(p,q,r);
%p A338262 m:= round(a);
%p A338262 if not isprime(m) then next fi;
%p A338262 d:= abs(a-m);
%p A338262 if is(d < dmin) then
%p A338262   count:= count+1;
%p A338262   dmin:= d;
%p A338262   R:= R, p;
%p A338262 fi
%p A338262 od:
%p A338262 R;
%o A338262 (PARI) lista(nn) = {my(m=p=3, q=5, s, t); print1(2); forprime(r=7, nn, s=sqrt((p-s=(p+q+r)/2)*(q-s)*(s-r)*s); if(m>t=min(s-precprime(s), nextprime(s)-s), print1(", ", p); m=t); p=q; q=r); } \\ _Jinyuan Wang_, Oct 24 2020
%Y A338262 Cf. A330096, A338267, A338269.
%K A338262 nonn,more
%O A338262 1,1
%A A338262 _J. M. Bergot_ and _Robert Israel_, Oct 19 2020
%E A338262 a(10)-a(16) from _Jinyuan Wang_, Oct 24 2020