cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A335992 Numbers that are the average of more pairs of distinct twin primes than any previous number.

This page as a plain text file.
%I A335992 #19 Aug 03 2020 15:35:47
%S A335992 1,4,8,12,24,57,105,150,330,645,666,945,1155,1770,1785,2625,2925,3255,
%T A335992 3465,5145,5460,5775,6930,8295,10605,11340,13650,15015,17205,18480,
%U A335992 19635,21945,27930,30030,38115,42735,45045,48840,51765,53130
%N A335992 Numbers that are the average of more pairs of distinct twin primes than any previous number.
%C A335992 Let T(n) be the number of pairs of twin primes (that is, primes p where p+2 or p-2 is also prime) with average n.  These are the positions at which T(n) attains high-water marks.
%H A335992 N. J. A. Sloane, <a href="/transforms.txt">Transforms</a> (The RECORDS transform returns both the high-water marks and the places where they occur).
%e A335992 1 is not the average of any pairs of twin primes.  4 is the average of one pair of twin primes: 3 and 5.  8 is the average of two pairs of twin primes: 5 and 11, and 3 and 13.  (Note that the difference between the twin primes in each pair is not necessarily 2.  However, both members of the pair are twin primes, that is, prime numbers p such that either p+2 or p-2 is also prime.  The fact that their twins are not part of the pair doesn't matter.)
%t A335992 m = 10^4; tp = Select[Range[3, m, 2], PrimeQ[#] && Or @@ PrimeQ[# + {-2, 2}] &]; f[n_] := Module[{k = Length @ IntegerPartitions[n, {2}, tp]}, If[MemberQ[tp, n/2], k - 1, k]]; s = {}; fm = 0; Do[f1 = f[n]; If[f1 > fm, fm = f1; AppendTo[s, n]], {n, 2, m/2, 2}]; Prepend[s/2, 1] (* _Amiram Eldar_, Jul 11 2020 *)
%Y A335992 The values attained at these high-water marks are given in A335993.
%Y A335992 Cf. A001097, A053033.
%K A335992 nonn
%O A335992 1,2
%A A335992 _P. Michael Kielstra_, Jul 04 2020