A370090 - OEIS

%I #45 Feb 17 2024 15:15:45

%S 5,7,8,9,10,12,13,14,15,19,21,25,31,33,38,39,43,45,49,55,61,63,69,73,

%T 75,81,85,91,99,103,105,109,111,115,129,133,139,141,151,153,159,165,

%U 169,175,181,183,193,195,199,201,213,225,229,231,235,241,243,253,259,265

%N Numbers that can be expressed in exactly one way as the unordered sum of two distinct primes.

%C Apparently, a number that is the predecessor or successor of a prime number does not have a sum as defined here, except for a finite number of primes, which may be {7, 11, 13, 37}. - _Peter Luschny_, Feb 16 2024

%H Michael S. Branicky, <a href="/A370090/b370090.txt">Table of n, a(n) for n = 1..10000</a>

%H <a href="/index/Go#Goldbach">Index entries for sequences related to Goldbach conjecture</a>

%H <a href="/index/Par#part">Index entries for sequences related to partitions</a>

%e 5 = 2+3; 7 = 2+5; 8 = 3+5; 9 = 2+7; 10 = 3+7 (10 = 5+5 is not considered).

%p select(n -> A117929(n) = 1, [seq(1..265)]);  # _Peter Luschny_, Feb 16 2024

%o (Python)

%o from sympy import sieve

%o from collections import Counter

%o from itertools import combinations

%o def aupton(max):

%o     sieve.extend(max)

%o     a = Counter(c[0]+c[1] for c in combinations(sieve._list, 2))

%o     return [n for n in range(1, max+1) if a[n] == 1]

%o print(aupton(265)) # _Michael S. Branicky_, Feb 16 2024

%Y Cf. A117929, A048974, A065091, A067187 (not necessarily distinct).

%Y If we change 1 way (this sequence) we get A077914 (2 ways), A077969 (3 ways), A078299 (4 ways), A080854 (5 ways), and A080862 (6 ways).

%K nonn

%O 1,1

%A _Wesley Ivan Hurt_, Feb 11 2024