[seqfan] Re: Reversing A281684.

[Michael Branicky]

Here are all n: f(n) with n in 1..100 s.t. f(n) <= 1000

{3: 2, 5: 646, 7: 6, 9: 302, 10: 24, 12: 6, 17: 17, 21: 46, 27: 110, 29:
62, 30: 572, 32: 105, 34: 2, 36: 105, 39: 2, 42: 322, 43: 2, 45: 14, 46:
150, 47: 475, 48: 2, 50: 9, 52: 70, 53: 228, 54: 172, 57: 2, 58: 136, 59:
10, 61: 30, 62: 199, 63: 4, 65: 2, 67: 2, 69: 13, 71: 155, 77: 239, 78:
188, 84: 182, 85: 62, 87: 4, 89: 2, 91: 7, 94: 227, 99: 360, 100: 542}

On Thu, Mar 4, 2021 at 7:07 PM cwwuieee <cwwuieee at gmail.com> wrote:

> f(11)=1388.
> -------- Original message --------From: michel.marcus at free.fr Date:
> 3/4/21  10:34 AM  (GMT-05:00) To: Sequence Fanatics Discussion list <
> seqfan at list.seqfan.eu> Subject: [seqfan] Reversing A281684. Dear Seqfans
> A281684 is defined as: Least composite k such that the concatenation of n
> consecutive composites, starting from k, is a prime. It has a few small
> values: A281684(2)= 8; A281684(6)= 14; A281684(14)= 15; A281684(24)= 18;
> A281684(302)= 16. So is it possible to reverse it ? f(n) = least number k
> such that the concatenation of k composite numbers starting from the n-th
> composite is prime f(3) = 2 2nd composite : 8 ; 89 is prime f(5) = 646 f(7)
> = 6 7th composite : 14 ; 141516182021 is prime f(8) = 14 f(9) = 302 f(10) =
> 24 Is it possible to find f(1), f(2), f(4), f(6) that are the first missing
> values for f() ? Best MM --Seqfan Mailing list - http://list.seqfan.eu/
>
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