# [seqfan] Re: A180268

Klaus Brockhaus klaus-brockhaus at t-online.de
Tue Aug 24 00:11:20 CEST 2010

```Richard Mathar schrieb:
> kb> %S A180268 988,1612,3172,5332,7852
> kb> %N A180268 Numbers n with property that A000203(n)-n-1 is a prime number
> kb> and 2*n+1-A000203(n) is a prime number.
>
> This should be something like (found be looking at other contemporary
> submissions of the author):
>
> %N A180268 Numbers n>10, not multiples of 6, such that A000203(n)-n-1 and 2*n+1-A000203(n) are prime numbers.
>
For
Numbers n>10, not multiples of 6, such that A000203(n)-n-1 and
2*n+1-A000203(n) are prime numbers
I get

70, 988, 1612, 3172, 3472, 5332, 5488, 7852, 11908, 15184, 15808, 18748,
19276, 21268, 21508, 24016, 25156, 25648, 29488, 30256, 32188, 35932,
36112,
36208, 37072, 38608, 39088, 41116, 41452, 42256, 43108, 43888, 46900,
47728,
48112, 50236, 54436, 55300, 55876, 57412, 62452, 65104, 65836, 70864,
71248,
72748, 74572, 80848, 85312, 85828, 88996, 96772, 97708, 98800, 99292

but for
Numbers n>10, not multiples of 6 and not multiples of 7, such that
A000203(n)-n-1 and 2*n+1-A000203(n) are prime numbers
I get

988, 1612, 3172, 5332, 7852, 11908, 15184, 15808, 18748, 19276, 21268,
21508,
24016, 25156, 29488, 30256, 32188, 35932, 36112, 36208, 38608, 41116,
41452,
42256, 43108, 43888, 47728, 48112, 50236, 54436, 55876, 57412, 62452,
65104,
65836, 70864, 71248, 72748, 74572, 80848, 85312, 85828, 88996, 96772,
97708,
98800, 99292

which is in agreement with the original terms. However, this seems to me
a rather arbitrary and contrived definition.

KB

```