OFFSET
1,1
COMMENTS
FORMULA
a(n) ~ n.
EXAMPLE
14 is in sequence because the list of divisors of 14: (1, 2, 7, 14) contains digit 7.
MATHEMATICA
Select[Range@108, Part[Plus @@ DigitCount@ Divisors@ #, 7] > 0 &]
PROG
(Magma) [n: n in [1..1000] | [7] subset Setseq(Set(Sort(&cat[Intseq(d): d in Divisors(n)])))]
(PARI) is(n)=fordiv(n, d, if(setsearch(Set(digits(d)), 7), return(1))); 0
(Python)
from itertools import count, islice
from sympy import divisors
def A257224_gen(): return filter(lambda n:any('7' in str(d) for d in divisors(n, generator=True)), count(1))
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Jaroslav Krizek, May 05 2015
EXTENSIONS
Mathematica and PARI programs with assistance from Michael De Vlieger and Charles R Greathouse IV, respectively.
STATUS
approved