# [seqfan] Re: A180268

hv at crypt.org hv at crypt.org
Tue Aug 24 11:02:09 CEST 2010

```Klaus Brockhaus <klaus-brockhaus at t-online.de> wrote:
: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.

70 is abundant, so 2n+1-sigma(n) < 0. I suspect it should be restricted
to deficient numbers, so that both quantities are positive.

But I'm not going to check whether that gives the correct figures.
It is a criminal waste of the valuable time of many fine mathematicians
for the list to try and reverse engineer the definitions for garbage
sequences like this: better would be to immediately delete the sequence
and return a form letter to the submitter saying "the entries in the