login
A089829
Triangle T(p,k) read by rows, where p runs through the odd primes and 2 <= k <= p-1. T(p,k) = 1 if the reverse of the base-k expansion of p is a prime, otherwise 0.
1
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 1, 1, 0, 1, 1, 0, 0, 1, 1, 1, 1, 0, 1, 1, 0, 1, 1, 0, 0, 1, 0, 1, 0, 1, 0, 0, 1, 1, 1, 0, 0, 1, 0
OFFSET
3,1
COMMENTS
Row p has p-2 terms.
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)".
LINKS
EXAMPLE
Writing 11 in bases 2 through 10, we obtain
1011,102,23,21,15,14,13,12,11. Reversing these, we obtain
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.
1,1,0,1,1,1,0,1,1
Triangle begins:
.1
.1 1 1
.1 1 1 1 1
.1 1 0 1 1 1 0 1 1
....
CROSSREFS
See A074481 for another version.
Sequence in context: A354924 A353799 A123927 * A294935 A242902 A196368
KEYWORD
base,easy,nonn,tabf
AUTHOR
Sam Alexander, Nov 12 2003
STATUS
approved