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, 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, 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, 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

Offset

2,1

Comments

Row p has p-1 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

Table of n, a(n) for n=2..106.

C. E. Nichols, Radiant Prime, 2003

Example

Writing 11 in bases 1 through 10, we obtain
11111111111,1011,102,23,21,15,14,13,12,11. Reversing these, we obtain
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.
1,1,1,0,1,1,1,0,1,1
Triangle begins:
.1
.1 1
.1 1 1 1
.1 1 1 1 1 1
.1 1 1 0 1 1 1 0 1 1
....

Crossrefs

See A089829 for another version.

Sequence in context: A189022 A370598 A166234 * A015420 A015522 A015658

Adjacent sequences: A074478 A074479 A074480 * A074482 A074483 A074484

Keyword

base,easy,nonn,tabf

Author

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

Extensions

More terms from Ray Chandler, Nov 22 2003

Status

approved