A280427 a(n) is a prime, such that a(n) = p^d-2 where p is a prime and d is the number of digits of p.

3, 5, 167, 359, 839, 1367, 1847, 2207, 3719, 5039, 7919, 1295027, 3442949, 9393929, 13997519, 21253931, 49430861, 84604517, 95443991, 237176657, 329939369, 384240581, 487443401, 633839777, 904231061, 1078193566319, 1427186233199, 1556727840719, 1985193642959

Offset: 1

Author

Sergey Pavlov, Jan 02 2017

Keywords

• nonn
• base

Comments

These numbers (proved for all p < 500) are a subset of A007528. For all even p, such numbers are a subset of A007528. The sequence is a subset of all numbers f(i) such that f(i) = i^d-2 (d - number of digits of integer i) and f(i) is a prime: e.g., f(15) is prime while f(15) = 15^2-2 = 223.

Examples

			If p=5, then d=1 and a(1)=3; if p=7, then d=1 and a(2)=5; if p=13, then d=2 and a(3)=167; etc.
		

Crossrefs

Cf. A007528.

Programs

Mathematica

Select[Array[#^IntegerLength@ # - 2 &@ Prime@ # &, 200], PrimeQ] (* Michael De Vlieger, Jan 03 2017 *)

Formula

a(n) = p^d-2, a(n) is prime, p is a prime and d is the number of digits of p.

Extensions

More terms from Michael De Vlieger, Jan 03 2017