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

1,1

Links

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

Example

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.

Prog

(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

Crossrefs

Intersection of A034710 and A061596.

Sequence in context: A061595 A062940 A061596 * A075813 A107952 A004032

Adjacent sequences: A061594 A061595 A061596 * A061598 A061599 A061600

Keyword

nonn,base

Author

Felice Russo, May 22 2001

Extensions

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

Status

approved