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.

A260310 Pairs with balanced sums of prime divisors (A008472) and inverse prime divisors (A069359), ordered by larger members.

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%I A260310 #32 Sep 26 2016 21:01:41
%S A260310 3,8,7,16,11,18,7,27,17,45,29,50,41,54,53,60,31,64,71,84,29,99,107,
%T A260310 132,61,147,41,153,131,162,53,207,157,220,113,225,179,228,239,240,131,
%U A260310 242,79,243,73,245,127,255,127,256,229,264,223,280,113,297,199,315,73,325,317,336,181,338,43,343,269,348
%N A260310 Pairs with balanced sums of prime divisors (A008472) and inverse prime divisors (A069359), ordered by larger members.
%C A260310 Consider pairs (x,y) of numbers where sum(p|x) p + sum(q|y) q = x*sum(p|x) 1/p + y*sum(q|y) 1/q where p, q are primes and sum(p|x) p > sum(q|y) q.
%C A260310 Or, pairs of numbers x and y where A008472(x) + A008472(y) = A069359(x) + A069359(y) where A008472(x) > A008472(y).
%C A260310 A001222(a(2n -1)) = 1 and A001222(a(2n)) >= 3.
%C A260310 For the vast majority of the time, a(2n-1) is prime. There seems to be about 1 pair per decade.
%C A260310 Conjecture: a(2n) < a(2n+2) for all n>0, but there are many times (1/10.84) that a(2n) + 1 = a(2n+2).
%C A260310 Conjecture: if a(2n-1) is prime then a(2n) is composite and vice versa. And when a(2n-1) is composite, it is congruent to 0 (mod 6). - _Robert G. Wilson v_, Jul 22 2015
%C A260310 The first conjecture appears to be satisfied because if both x and y were prime then the sum of the A008472 were the sum of the two primes and the sum of the A069359 were two. - _R. J. Mathar_, Aug 03 2015
%H A260310 Robert G. Wilson v, <a href="/A260310/b260310.txt">Table of n, a(n) for n = 1..19812</a>
%e A260310 3 and 8 is first pair of this sequence because A008472(3) + A008472(8) = 3 + 2 = 5 is equal to A069359(3) + A069359(8) = 1 + 4 = 5.
%t A260310 f[n_] := f[n] = Block[{fi = FactorInteger[n][[All, 1]]}, {Plus @@ fi, n*Plus @@ (1/fi)}] /; n > 0; k =3; lst = {}; While[ k < 400, j = 2; While[ j < k, If[ f[k][[1]] + f[j][[1]] == f[k][[2]] + f[j][[2]] && f[k][[1]] != f[k][[2]], AppendTo[lst, {j,k}]]; j++]; k++]; lst // Flatten (* _Robert G. Wilson v_, Jul 22 2015 *)
%Y A260310 Cf. A001222, A008472, A069359.
%K A260310 nonn
%O A260310 1,1
%A A260310 _Juri-Stepan Gerasimov_, Jul 22 2015
%E A260310 Corrected and edited by _Robert G. Wilson v_, Jul 22 2015