OFFSET
1,2
COMMENTS
The sequence is given for 7-segment displays that format their digits like so:
_ _ _ _ _ _ _ _
| | | _| _| |_| |_ |_ | |_| |_|
|_| | |_ _| | _| |_| | |_| _|
.
This sequence is infinite: For any n let e := Sum_{i=0..n} 2*4^i (2, 10, 42, ... see A020988). The number a := 4*10^e is a member of the sequence. It has 4+6*e active segments (one four and e noughts).
The numbers 4, 5 and 6 are the only entries that exactly equal their count of active segments.
REFERENCES
Heureka - Mathematische Rätsel 2021 - Tageskalender, Anaconda-Verlag, 2020, ISBN-978-3-7306-0881-4.
LINKS
PROG
(Python)
def filter(n):
seg = 0
for c in str(n):
seg += { 0: 6, 1: 2, 2: 5, 3: 5, 4: 4, 5: 5, 6: 6, 7: 3, 8: 7, 9: 6 }[int(c)]
return(n % seg == 0)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Marian Aldenhövel and Florentin Aldenhövel, Jun 30 2021
STATUS
approved