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

12, 20, 28, 63, 44, 52, 117, 68, 76, 171, 92, 207, 345, 116, 124, 279, 465, 148, 333, 164, 172, 387, 188, 423, 705, 212, 477, 795, 236, 244, 549, 915, 268, 603, 284, 292, 657, 1095, 316, 711, 332, 747, 1245, 356, 801, 1335, 1869, 388

Offset: 3

Author

Omar E. Pol, Jun 29 2012

Keywords

• nonn
• look

Comments

From Robert Israel, May 24 2019: (Start)

If p is an odd prime, then a((p+3)/2) = 4*p.

If p > 2 is in A067774, then a((p+5)/2) = 9*p. (End)

Links

• Robert Israel, Table of n, a(n) for n = 3..10000

Crossrefs

Cf. A067774, A210967.

Programs

Maple

N:= 100: # for a(3)..a(N)
P:= select(isprime, [2,seq(i,i=3..2*N+1,2)]): nP:= nops(P):
A:= Vector([infinity$(2*N+1)]):
for i from 1 to nP while 2*P[i] <= 2*N+1 do
   p:= P[i];
   for j from i to nP while p+P[j] <= 2*N+1 do
     if p*P[j] < A[p+P[j]] then A[p+P[j]]:= p*P[j] fi
od od:
B:= Vector([infinity$(2*N+1)]):
for i from 1 to nP while 3*P[i] <= 2*N+1 do
  p:= P[i];
  for x from 4 to 2*N+1-p do
    y:= p+x;
    if A[x]*p < B[y] then B[y]:= A[x]*p fi
od od:
[seq(B[2*i+1],i=3..N)]; # Robert Israel, May 24 2019