login
This site is supported by donations to The OEIS Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A105173 Numbers n such that either n*(n+1)/4 + 1 or n*(n+1)/4 - 1 or both are primes. 0
3, 7, 8, 15, 16, 23, 24, 32, 39, 40, 47, 48, 55, 56, 63, 64, 71, 79, 80, 87, 95, 103, 104, 111, 112, 119, 120, 128, 135, 136, 143, 151, 152, 159, 167, 175, 176, 183, 199, 208, 216 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The primes are = (sum of numbers from 1 to n)/2 + or - 1

LINKS

Table of n, a(n) for n=1..41.

EXAMPLE

3*4/4=3 3-1=2 prime so a(1)=3

7*8/4=14 14-1=13 prime so a(2)=7

8*9/4=18 18-1=17 prime 18+1=19 prime so a(3)=8

CROSSREFS

Sequence in context: A002381 A131559 A051211 * A309197 A076683 A045542

Adjacent sequences:  A105170 A105171 A105172 * A105174 A105175 A105176

KEYWORD

nonn

AUTHOR

Pierre CAMI, Apr 11 2005

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 7 18:12 EST 2019. Contains 329847 sequences. (Running on oeis4.)