cp's OEIS Frontend

A210968 Smallest prime product p*q*r such that p + q + r = 2*n + 1.

%I A210968 #14 May 25 2019 02:35:03
%S A210968 12,20,28,63,44,52,117,68,76,171,92,207,345,116,124,279,465,148,333,
%T A210968 164,172,387,188,423,705,212,477,795,236,244,549,915,268,603,284,292,
%U A210968 657,1095,316,711,332,747,1245,356,801,1335,1869,388
%N A210968 Smallest prime product p*q*r such that p + q + r = 2*n + 1.
%C A210968 From _Robert Israel_, May 24 2019: (Start)
%C A210968 If p is an odd prime, then a((p+3)/2) = 4*p.
%C A210968 If p > 2 is in A067774, then a((p+5)/2) = 9*p. (End)
%H A210968 Robert Israel, <a href="/A210968/b210968.txt">Table of n, a(n) for n = 3..10000</a>
%p A210968 N:= 100: # for a(3)..a(N)
%p A210968 P:= select(isprime, [2,seq(i,i=3..2*N+1,2)]): nP:= nops(P):
%p A210968 A:= Vector([infinity$(2*N+1)]):
%p A210968 for i from 1 to nP while 2*P[i] <= 2*N+1 do
%p A210968    p:= P[i];
%p A210968    for j from i to nP while p+P[j] <= 2*N+1 do
%p A210968      if p*P[j] < A[p+P[j]] then A[p+P[j]]:= p*P[j] fi
%p A210968 od od:
%p A210968 B:= Vector([infinity$(2*N+1)]):
%p A210968 for i from 1 to nP while 3*P[i] <= 2*N+1 do
%p A210968   p:= P[i];
%p A210968   for x from 4 to 2*N+1-p do
%p A210968     y:= p+x;
%p A210968     if A[x]*p < B[y] then B[y]:= A[x]*p fi
%p A210968 od od:
%p A210968 [seq(B[2*i+1],i=3..N)]; # _Robert Israel_, May 24 2019
%Y A210968 Cf. A067774, A210967.
%K A210968 nonn,look
%O A210968 3,1
%A A210968 _Omar E. Pol_, Jun 29 2012