A298990 Least number m such that A035026(m) = n.

1, 2, 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

Offset: 0

Author

Seiichi Manyama, Jan 31 2018

Keywords

• nonn

Comments

The upper branch visible in the scatterplot of the first terms corresponds to odd-indexed terms. - Rémy Sigrist, Jan 31 2018

Examples

			2* 2 = 2 +  2,                                      so a(1) =  2.
2* 4 = 3 +  5 = 5 +  3,                             so a(2) =  4.
2* 5 = 3 +  7 = 5 +  5 =  7 +  3,                   so a(3) =  5.
2* 8 = 3 + 13 = 5 + 11 = 11 +  5 = 13 + 3,          so a(4) =  8.
2*11 = 3 + 19 = 5 + 17 = 11 + 11 = 17 + 5 = 19 + 3, so a(5) = 11.
		

Links

• Rémy Sigrist, Table of n, a(n) for n = 0..10000
• Rémy Sigrist, C++ program for A298990

Crossrefs

Cf. A035026.

Programs

PARI

nb(n) = sum(i=1, 2*n-1, isprime(i) && isprime(2*n-i));
a(n) = {my(k=1); while (nb(k) != n, k++); k;} \\ Michel Marcus, Jan 31 2018