[seqfan] Re: Like A6919, but starting with 20

[M. F. Hasler]

Yes, Alonso, i think you got that right and your last term (33...13) is
indeed a prime.

Sequence A037271 gives the number of steps until a prime is reached - when
starting with the n-the composite number.

I think it would have been better to start simply with n and have a(p)=1
for primes p...
If I'm not wrong that would yield
1, 1, 1, 3, 1, 2, 1, 14, 3, 5, 1, 2, 1, 6, 5, 5, 1, 2, 1, 16,...
which is not in OEIS.

- Maximilian

(PARI) \\ a(n) from https://oeis.org/A037276
L(n)=for(i=1,oo,n==(n=a(n))&& return(i))

apply(L,[1..20])
= [1, 1, 1, 3, 1, 2, 1, 14, 3, 5, 1, 2, 1, 6, 5, 5, 1, 2, 1, 16]


On Fri, Oct 7, 2022, 10:19 Alonso Del Arte <alonso.delarte at gmail.com> wrote:

>  The 13th term of A6919 is a prime number, thereby reaching a fixed point.
> I've played around with similar sequences with different starting points.
> Most of the ones I've looked at quickly reach a prime. But the one starting
> with 20, if my calculations are correct, goes like this
>
> 20, 225, 3355, 51161, 114651, 3312739, 17194867, 194122073, 709273797,
> 39713717791, 113610337981, 733914786213, 3333723311815403,
> 131723655857429041, 772688237874641409, 3318308475676071413
>
> I do believe this one too reaches a prime eventually. Can someone verify
> what I've got so far?
>
> Al
>