|
|
A357823
|
|
a(n) is the number of bases > 1 where n is not divisible by the sum of its digits.
|
|
2
|
|
|
0, 0, 1, 0, 3, 0, 5, 1, 4, 3, 9, 1, 11, 9, 7, 5, 15, 5, 17, 7, 11, 17, 21, 5, 18, 20, 17, 14, 27, 12, 29, 16, 24, 28, 24, 13, 35, 33, 31, 17, 39, 22, 41, 33, 26, 41, 45, 18, 42, 34, 42, 38, 51, 33, 45, 35, 48, 53, 57, 26, 59, 57, 44, 41, 52, 43, 65, 56, 60, 48
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,5
|
|
COMMENTS
|
The sequence is well defined as the sum of digits of n equals n (and hence divides n) in any base > n.
|
|
LINKS
|
|
|
FORMULA
|
a(p) = p - 2 for any prime number p.
|
|
EXAMPLE
|
For n = 10, we have:
b sum of digits divisible?
---- ------------- ----------
2 2 Yes
3 2 Yes
4 4 No
5 2 Yes
6 5 Yes
7 4 No
8 3 No
9 2 Yes
10 1 Yes
>=11 10 Yes
so a(n) = #{ 4, 7, 8 } = 3.
|
|
MATHEMATICA
|
NivenQ[n_, b_] := Divisible[n, Total @ IntegerDigits[n, b]]; a[n_] := Sum[Boole @ !NivenQ[n, b], {b, 2, n}]; Array[a, 70]
|
|
PROG
|
(PARI) a(n) = sum(b=2, n, n%sumdigits(n, b)!=0)
(Python)
from sympy.ntheory.factor_ import digits
def A357823(n): return sum(1 for b in range(2, n) if n%sum(digits(n, b)[1:])) # Chai Wah Wu, Oct 19 2022
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,base
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|