A244607 Numbers k such that (product of digits of k) - 1 is prime.

3, 4, 6, 8, 13, 14, 16, 18, 22, 23, 24, 26, 27, 29, 31, 32, 34, 36, 38, 41, 42, 43, 45, 46, 48, 54, 56, 61, 62, 63, 64, 65, 67, 68, 69, 72, 76, 81, 83, 84, 86, 89, 92, 96, 98, 113, 114, 116, 118, 122, 123, 124, 126, 127, 129, 131, 132, 134, 136, 138, 141, 142, 143, 145, 146

Offset: 1

Author

Derek Orr, Jul 01 2014

Keywords

• nonn
• base
• easy

Comments

This sequence is infinite. With any number a(n), you can add infinitely many 1's to its decimal representation. E.g., 32 is in this sequence, so 321, 312, 3211, 32111, 31121, 11321, etc. are also terms of this sequence.

A number k is a term of this sequence iff A007954(k) is in A008864.

Examples

			3*2 - 1 = 5 is prime. Thus 32 is a term of this sequence.
		

Links

• Jens Kruse Andersen, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A007954, A008864, A089377, A081988.

Programs

PARI

for(n=1,10^3,d=digits(n);p=prod(i=1,#d,d[i]);if(isprime(p-1),print1(n,", ")))

Extensions

Wrong term removed by Jens Kruse Andersen, Jul 13 2014