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.

A023036 Smallest positive even integer that is an unordered sum of two primes in exactly n ways.

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%I A023036 #49 Nov 03 2023 06:37:57
%S A023036 2,4,10,22,34,48,60,78,84,90,114,144,120,168,180,234,246,288,240,210,
%T A023036 324,300,360,474,330,528,576,390,462,480,420,570,510,672,792,756,876,
%U A023036 714,798,690,1038,630,1008,930,780,960,870,924,900,1134,1434,840,990,1302,1080
%N A023036 Smallest positive even integer that is an unordered sum of two primes in exactly n ways.
%C A023036 Except for first two terms, same as A001172.
%C A023036 The first occurrence of k in A045917.
%C A023036 The graph looks like a comet. - _Daniel Forgues_, Jun 12 2014
%H A023036 Robert G. Wilson v, <a href="/A023036/b023036.txt">Table of n, a(n) for n = 0..10000</a> (first 1001 terms from T. D. Noe)
%H A023036 <a href="/index/Go#Goldbach">Index entries for sequences related to Goldbach conjecture</a>
%e A023036 a(3) = 22 as 22 = (19+3) = (17+5) = (11+11). There are exactly 3 ways 22 can be expressed as the sum of two primes and no even number less than 22 can be so expressed.
%e A023036 From _Daniel Forgues_, Jun 13 2014: (Start)
%e A023036 Terms for n = 1..6 and corresponding sums:
%e A023036   a(1) =  4 =  2 + 2;
%e A023036   a(2) = 10 =  7 + 3 =  5 +  5;
%e A023036   a(3) = 22 = 19 + 3 = 17 +  5 = 11 + 11;
%e A023036   a(4) = 34 = 31 + 3 = 29 +  5 = 23 + 11 = 17 + 17;
%e A023036   a(5) = 48 = 43 + 5 = 41 +  7 = 37 + 11 = 31 + 17 = 29 + 19;
%e A023036   a(6) = 60 = 53 + 7 = 47 + 13 = 43 + 17 = 41 + 19 = 37 + 23 = 31 + 29.
%e A023036 (End)
%t A023036 f[n_] := Length@ Select[2n - Prime@ Range@ PrimePi@ n, PrimeQ]; nn = 100; t = Table[0, {nn}]; k = 1; cnt = 0; While[cnt < nn, a = f@k; If[a <= nn && t[[a]] == 0, t[[a]] = 2 k; cnt++]; k++]; t (* _Robert G. Wilson v_, Mar 15 2011 *)
%Y A023036 Cf. A045917, A000954, A136244, A258713.
%K A023036 nonn,look
%O A023036 0,1
%A A023036 _David W. Wilson_, Jun 14 1998