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.

A294113 Sum of the smaller parts of the partitions of 2n into two parts with larger part prime.

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%I A294113 #21 Mar 14 2018 03:54:39
%S A294113 0,3,4,4,8,6,11,8,13,20,28,24,32,25,32,41,51,42,51,40,49,60,72,60,72,
%T A294113 84,97,111,125,109,124,107,121,136,152,169,188,169,187,206,226,204,
%U A294113 224,199,218,238,258,229,248,268,289,312,336,306,331,357,384,412
%N A294113 Sum of the smaller parts of the partitions of 2n into two parts with larger part prime.
%H A294113 Robert Israel, <a href="/A294113/b294113.txt">Table of n, a(n) for n = 1..10000</a>
%H A294113 <a href="/index/Par#part">Index entries for sequences related to partitions</a>
%F A294113 a(n) = Sum_{i=1..n} i * A010051(2n-i).
%F A294113 a(n) = 2*n*(A000720(2*n)-A000720(n-1)) - A034387(2*n) + A034387(n-1) for n >= 2. - _Robert Israel_, Mar 13 2018
%e A294113 For n=7, 2n = 14 can be partitioned into two parts with the larger part prime as 13 + 1, 11 + 3, and 7 + 7. So a(7) = 1 + 3 + 7 = 11. - _Michael B. Porter_, Mar 14 2018
%p A294113 N:= 1000: # to get a(1)..a(n)
%p A294113 P:= select(isprime, [2,seq(i,i=3..2*N,2)]):
%p A294113 S:= ListTools:-PartialSums(P):
%p A294113 f:= proc(n) local k1,k2;
%p A294113      k1:= numtheory:-pi(2*n);
%p A294113      k2:= numtheory:-pi(n-1);
%p A294113      2*n*(k1-k2) - S[k1] + S[k2]
%p A294113 end proc:
%p A294113 f(1):= 0:
%p A294113 seq(f(n),n=1..N); # _Robert Israel_, Mar 13 2018
%t A294113 Table[Sum[i (PrimePi[2 n - i] - PrimePi[2 n - i - 1]), {i, n}], {n, 80}]
%o A294113 (PARI) a(n) = sum(k=1, n, k*isprime(2*n-k)); \\ _Michel Marcus_, Oct 24 2017
%o A294113 (PARI) a(n) = my(res = 0); forprime(p = n, 2*n, res+=(2*n - p)); res \\ _David A. Corneth_, Oct 24 2017
%Y A294113 Cf. A000720, A010051, A034387, A294114.
%K A294113 nonn,easy
%O A294113 1,2
%A A294113 _Wesley Ivan Hurt_, Oct 22 2017