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

 

Logo

The October issue of the Notices of the Amer. Math. Soc. has an article about the OEIS.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A074481 Triangle T(p,k) read by rows, where p runs through the primes and 1 <= k <= p-1. T(p,k) = 1 if the reverse of the base-k expansion of p is a prime, otherwise 0. 1

%I

%S 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,1,1,1,0,1,1,1,1,1,1,1,0,1,1,1,1,1,

%T 1,1,1,0,1,1,0,1,0,1,1,1,1,1,1,1,1,1,0,1,0,1,0,1,0,1,0,1,0,1,1,1,0,0,

%U 1,1,1,1,1,1,0,1,0,1,0,1,0,1,1,0,1,1,0,0,1,1,1,1,1,0,1,1,0,1,1,0,0,1,0,1,0

%N Triangle T(p,k) read by rows, where p runs through the primes and 1 <= k <= p-1. T(p,k) = 1 if the reverse of the base-k expansion of p is a prime, otherwise 0.

%C Row p has p-1 terms.

%C A very large version of this pyramid, with 1's replaced with white dots and 0's replaced with black dots, shows a very interesting pattern (see link). The author says: "These primes form a pattern similar to an astronomical radiant (the point in the sky from which a meteor shower appears to originate)".

%H C. E. Nichols, <a href="http://www.radiantprimes.com/">Radiant Prime</a>, 2003

%e Writing 11 in bases 1 through 10, we obtain

%e 11111111111,1011,102,23,21,15,14,13,12,11. Reversing these, we obtain

%e 11111111111,1101,201,32,12,51,41,31,21,11. Now 32 (base 4) and 31 (octal) are composite, all others are prime, so the row for 11 reads.

%e 1,1,1,0,1,1,1,0,1,1

%e Triangle begins:

%e .1

%e .1 1

%e .1 1 1 1

%e .1 1 1 1 1 1

%e .1 1 1 0 1 1 1 0 1 1

%e ....

%Y See A089829 for another version.

%K base,easy,nonn,tabf

%O 2,1

%A C. E. Nichols (radprime(AT)radiantprimes.com), Nov 19 2003

%E More terms from _Ray Chandler_, Nov 22 2003

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 25 01:17 EDT 2018. Contains 315360 sequences. (Running on oeis4.)