A083992 a(1) = 1; then the smallest number such that both the forward and reverse n-th partial concatenation is a prime for n > 1. (Reverse concatenation is taken term-wise and not digit-wise.)

1, 1, 3, 11, 13, 47, 67, 213, 99, 753, 861, 143, 2187, 249, 193, 2957, 14553, 1557, 2359, 8669, 1491, 1003, 12131, 583, 2643, 3857, 5631, 999, 9693, 10231, 1451, 16861, 6321, 14567, 21649, 7563, 40983, 123, 12579, 57927, 4257, 6777, 359, 3679, 1191, 10139

Offset

0,3

Links

Table of n, a(n) for n=0..45.

Example

Both 1131113 and 1311311 are primes as a forward and reverse concatenation of the first five terms (1,1,3,11,13).

Crossrefs

Cf. A083993, A083994.

Sequence in context: A225097 A079665 A281728 * A370488 A105290 A201426

Adjacent sequences: A083989 A083990 A083991 * A083993 A083994 A083995

Keyword

base,hard,nonn

Author

Amarnath Murthy, May 23 2003

Extensions

More terms from Ray Chandler, Aug 03 2003

Status

approved