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A355484
a(n) is the least positive number that can be represented in exactly n ways as 2*p+q where p and q are primes.
1
1, 6, 9, 21, 17, 33, 45, 51, 75, 99, 111, 93, 105, 135, 153, 201, 165, 249, 231, 237, 321, 225, 273, 363, 411, 393, 285, 315, 471, 483, 435, 405, 465, 555, 681, 495, 783, 675, 873, 849, 963, 1729, 585, 525, 897, 795, 1041, 915, 735, 855, 1191, 825, 765, 1095, 975, 1005, 1035, 1125, 1311, 1407
OFFSET
0,2
COMMENTS
a(n) is the least number k such that A046926(k) = n.
LINKS
EXAMPLE
a(3) = 21 because 21 can be written as 2*p+q with p and q prime in exactly 3 ways, namely 21 = 2*2+17 = 2*5+11 = 2*7+7, and no smaller number works.
MAPLE
M:= 3000: # to use primes up to M
P:= select(isprime, [2, seq(i, i=3..M, 2)]): nP:= nops(P):
A:= Vector(M):
for i from 1 do
p:= P[i];
if 2*p >= M then break fi;
for j from 1 to nP do
q:= P[j];
v:= 2*p+q;
if v > M then break fi;
A[v]:= A[v]+1;
od od:
K:= max(A):
V:= Array(0..K+1):
for i from 1 to M do
if V[A[i]] = 0 then V[A[i]]:= i fi
od:
L:= min(select(t -> V[t] = 0, [$1..K+1])):
convert(V[0..L-1], list);
CROSSREFS
Sequence in context: A096546 A376472 A357840 * A358222 A165717 A239874
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Jul 03 2022
STATUS
approved