A076056 Primes which when read backwards are composite numbers.

19, 23, 29, 41, 43, 47, 53, 59, 61, 67, 83, 89, 103, 109, 127, 137, 139, 163, 173, 193, 197, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 317, 331, 349, 367, 379, 397, 401, 409, 419, 421, 431, 433, 439, 443, 449, 457

Offset: 1

Author

Amarnath Murthy, Oct 04 2002

Keywords

• base
• nonn

Comments

Subsidiary sequences that could be added:(1) Start of the first occurrence of n consecutive primes in the above sequence. (2) Start of the first occurrence of n consecutive primes with digit reversal also a prime.

The subsidiary sequence (1) with the indices at which n>=2 consecutive primes are first found in this sequence is 1, 1, 4, 4, 4, 4, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, ... - R. J. Mathar, May 22 2009

Subsequence of A151768. - Reinhard Zumkeller, Jul 06 2009

Links

• Anders Hellström, Table of n, a(n) for n = 1..10000
• Anders Hellström, Sage program

Crossrefs

Cf. A076055.

Complement of A007500 with respect to A000040. [From Reinhard Zumkeller, Jul 06 2009]

Programs

Magma

[p: p in PrimesUpTo(500)|not IsPrime(Seqint(Reverse(Intseq(p))))]; // Vincenzo Librandi, Jun 03 2019

Mathematica

Select[Prime[Range[100]], !PrimeQ[FromDigits[Reverse[IntegerDigits[ # ]]]]&]

Extensions

More terms from Harvey P. Dale, Oct 11 2002