OFFSET
1,2
EXAMPLE
For k = 13, the additive digital root = 4. (12 mod 4) = 0 and (14 mod 4) = 2, and thus 13 is a sequence entry.
For k = 31, the additive digital root = 4. (30 mod 4) = 2 and (32 mod 4) = 0, so 31 is a sequence entry.
For k = 23, the additive digital root = 5. (22 mod 5) = 2 and (24 mod 5) = 4, so 23 is not a sequence entry.
MATHEMATICA
Select[Range[1, 300, 2], !Divisible[#, 5] && (Divisible[# - 1, (dr = Mod[# - 1, 9] + 1)] || Divisible[# + 1, dr]) &] (* Amiram Eldar, Oct 02 2020 *)
PROG
(PARI) genit(maxx)={if(maxx<11, maxx=11); for (n=1, maxx, if(n%2==0 ||n%5==0, next); dr=(n-1)%9+1; if( (n+1)%dr==0 ||(n-1)%dr==0, print1(n, ", "))); }
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Bill McEachen, Sep 22 2020
STATUS
approved