A064539 All...are divisible by 3 but why?

[Ralf Stephan]

Zak,
for the primes are primes in all bases, the primes are not 'base'.
But if you have the sequence 'sum of digits is prime' then one must
know the base of the digits (usually 10) so that would be 'base'.
So whenever you do something with digits please add 'base'. 

Why 'base' sequences are uninteresting, I can give you one reason:
we like to find formulas for and interconnections between sequences, 
it's a real sport here. The problem: most 'base' sequences don't have
these or they are really simple, like 10^n-1 for all-nines or so.
But to get the difficult ones, it is better to study base-2 sequences
first because they are easier to tackle than base-10. So, 'base-10' is 
either too easy or too difficult so most of us dismiss them altogether.

I mean, what can be more satisfying than putting an %F line... ahm a
formula on a previously untouched sequence?


ralf