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

1,1

Links

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

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.

Example

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

Mathematica

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

Prog

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

Crossrefs

Cf. A060418.

Sequence in context: A354726 A235473 A137415 * A107200 A079823 A107156

Adjacent sequences: A090191 A090192 A090193 * A090195 A090196 A090197

Keyword

easy,nonn,base

Author

Enoch Haga, Jan 22 2004

Status

approved