OFFSET
1,1
COMMENTS
Equivalently, Bogotá numbers that are not Colombian and that can be written as (m + product of digits of m) for some m.
EXAMPLE
4 = 2 + 2 = 2 + 2 = 2 * 2;
16 = 8 + 8 = 8 + 8 = 4 * 4;
24 = 21 + (2+1) = 17 + (1*7) = 12 * (1*2);
56 = 46 + (4+6) = 51 + (5*1) = 14 * (1*4);
81 = 72 + (7+2) = 63 + (6*3) = 9 * 9.
MATHEMATICA
m = 2100; Select[Intersection @@ Union /@ Transpose[Table[{n + Plus @@ (d = IntegerDigits[n]), n + (p = Times @@ d), n*p}, {n, 1, m}]], # <= m &] (* Amiram Eldar, Sep 18 2020 *)
PROG
(PARI) isok(m) = {if (m==0, return (1)); for (k=1, m, if (k+vecprod(digits(k)) == m, return (1)); ); } \\ A337718
listb(nn) = Vec(setintersect(Set(vector(nn, k, k+sumdigits(k))), Set(vector(nn, k, k*vecprod(digits(k)))))); \\ A336983
lista(nn) = select(x->isok(x), listb(nn)); \\ Michel Marcus, Sep 18 2020
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Bernard Schott, Sep 18 2020
EXTENSIONS
More terms from Michel Marcus, Sep 18 2020
STATUS
approved