A378917 a(n) is the smallest positive integer having n decompositions of twice its value into ordered sums of two odd primes.
1, 3, 4, 5, 8, 11, 12, 17, 18, 37, 24, 53, 30, 89, 39, 71, 42, 101, 45, 179, 57, 137, 72, 193, 60, 233, 84, 257, 90, 251, 117, 401, 123, 311, 144, 373, 120, 347, 105, 457, 162, 661, 150, 479, 180, 547, 237, 599, 165, 617, 264, 641, 288, 683, 195, 907, 231, 881, 240, 773, 210
Offset: 0
Keywords
Examples
For n = 3 we have that the first 3 in A002372 has index 5 and twice 5 is 10 and 10 has 3 decompositions into ordered sums of two odd primes as follows: [3 + 7], [5 + 5], [7 + 3], so a(3) = 5.
Programs
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PARI
isop(n) = (n % 2) && isprime(n); nb(n) = n*=2; sum(i=1, n-1, isop(i)*isop(n-i)); \\ A002372 a(n) = my(k=1); while(nb(k) != n, k++); k; \\ Michel Marcus, Dec 14 2024
Extensions
More terms from Michel Marcus, Dec 14 2024
Comments