A090194 Primes which when multiplied by their largest digit and 1 is added form another prime.

2, 43, 61, 263, 433, 461, 601, 641, 653, 661, 821, 857, 1061, 1063, 1187, 1361, 1423, 1487, 1613, 1811, 1871, 1877, 2063, 2081, 2143, 2161, 2621, 2801, 2837, 3061, 3163, 3581, 3623, 3631, 3643, 3851, 4561, 5087, 5261, 5381, 5623, 5807, 5861, 6011, 6053

Offset: 1

Author

Enoch Haga, Jan 22 2004

Keywords

• easy
• nonn
• base

Examples

			a(2)=43. Largest digit is 4. Multiply 43*4=172. 172+1=173, prime.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A060418.

Programs

Mathematica

Select[Prime[Range[1000]],PrimeQ[1+#*Max[IntegerDigits[#]]]&] (* Harvey P. Dale, May 21 2024 *)

PARI

isok(p) = isprime(p) && isprime(p*vecmax(digits(p))+1); \\ Michel Marcus, Jun 08 2014

Formula

In the prime sequence, select largest digit in each prime, multiply by the prime containing that digit, then add 1. If the result is another prime, add to sequence.