A061597 Numbers whose sum of digits s equals its product of digits and s + 1 and s - 1 are both prime.

4, 6, 22, 123, 132, 213, 231, 312, 321, 111126, 111162, 111216, 111261, 111612, 111621, 112116, 112161, 112611, 116112, 116121, 116211, 121116, 121161, 121611, 126111, 161112, 161121, 161211, 162111, 211116, 211161, 211611, 216111, 261111, 611112

Offset: 1

Author

Felice Russo, May 22 2001

Keywords

• nonn
• base

Examples

			22 belong to the sequence because (2*2)+1=5, (2*2)-1=3, (2+2)+1=5, (2+2)-1=3 and 2+2=2*2.
		

Links

• Harry J. Smith, Table of n, a(n) for n = 1..81

Crossrefs

Intersection of A034710 and A061596.

Programs

PARI

isok(k) = my(d=digits(k), s=vecsum(d)); s == vecprod(d) && isprime(s+1) && isprime(s-1) \\ Harry J. Smith, Jul 25 2009

Extensions

4 and 6 added by Abdul Gaffar Khan, Nov 29 2015