A143738 Number of twin primes between n and n^2. Only smaller of twins (terms of A001359) are counted.

0, 1, 2, 2, 3, 3, 4, 5, 6, 6, 8, 8, 9, 11, 12, 14, 16, 16, 17, 17, 19, 20, 21, 22, 24, 26, 26, 26, 29, 30, 30, 31, 34, 36, 36, 39, 41, 42, 45, 45, 48, 49, 50, 53, 55, 59, 61, 63, 66, 66, 68, 70, 74, 74, 76, 77, 78, 83, 87, 90, 91, 93, 96, 100

Offset: 1

Author

Alen Skugor (askugor(AT)gmail.com), Aug 30 2008

Keywords

• nonn

Examples

			For n = 6, between 6 and 36 the smaller of twin pairs are {11, 17, 29}, so a(6) = 3.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A001359, A080356.

Programs

Magma

[#[p:p in PrimesInInterval(n,n^2)|IsPrime(p+2)]:n in [1..80]]; // Marius A. Burtea, Dec 20 2019

Mathematica

Table[Count[Table[PrimeQ[j] && PrimeQ[j + 2], {j, n, n*n}], True], {n, 1, 100}]