A115095 Positions of 4's in A038800 with offset 1.

1, 2, 11, 20, 83, 149, 188, 209, 326, 347, 566, 944, 1301, 1565, 1574, 1607, 1805, 1892, 1943, 2102, 2228, 2531, 3173, 3485, 4379, 5135, 5534, 6299, 6722, 6950, 7223, 7727, 7970, 8105, 8273, 8882, 9785, 9914, 10112, 10985, 11654, 11930, 12221, 13547

Offset: 1

Author

Zak Seidov, Mar 01 2006

Keywords

• nonn

Comments

Starting with a(2)=2, numbers m such that 10*(m-1)+{1,3,7,9} are all primes.

Essentially the same as A064975. - R. J. Mathar, Aug 11 2008

Examples

			11 is a term because 10*(11-1)+{1,3,7,9} = 101,103,107,109 are all prime.
		

References

• 4 is the maximum possible number of primes between 10*n and 10*(n+1).

Links

• Paolo Xausa, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A064975 (essentially the same).

Cf. A038800 (number of primes between 10*n and 10*n+9).

Cf. A007811.

Programs

Mathematica

Join[{1}, Select[Range[2, 15000, 3], AllTrue[10*# - {1, 3, 7, 9}, PrimeQ] &]] (* Paolo Xausa, Jul 15 2025 *)

Formula

a(1) = 1; for n >= 2, a(n) = A007811(n-1) + 1. - Paolo Xausa, Jul 15 2025

Extensions

Name edited by Paolo Xausa, Jul 20 2025