

A174402


Primes such that applying "reverse and add" twice produces two more primes


0



271, 281, 21491, 21991, 22091, 22481, 23081, 23971, 24071, 25951, 26681, 26981, 27271, 27431, 27691, 27791, 28031, 28661, 28921, 28961, 29021, 29191, 29251, 29411, 29671, 2129891, 2131991, 2141791, 2141891, 2151791, 2157091, 2161591, 2179391, 2191291
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OFFSET

1,1


COMMENTS

Some observations:
1. For all terms, the first digit is 2, last digit is 1, number of digits is odd: 3,5,7,...
2. The sequence is infinite. Number of 3digit terms is 2, number of 5digit terms is 23, number of 7digit terms is 585, number of 9digit terms is 26611.
3. Applying "reverse and add" a third time always produces composites.  Zak Seidov, Dec 09 2013


LINKS

Table of n, a(n) for n=1..34.


EXAMPLE

21491 is included because (1) it is prime, and (2) 21491 + 19412 = 40903 which is prime, and (3) 40903 + 30904 = 71807 which also is prime.


MATHEMATICA

Transpose[Select[Table[{Prime[i], And@@PrimeQ/@NestList[#+FromDigits[ Reverse[ IntegerDigits[#]]]&, Prime[i], 2]}, {i, 500000}], #[[2]] == True&]][[1]]


CROSSREFS

Cf. A061783.
Sequence in context: A290643 A104844 A086003 * A048295 A257210 A020363
Adjacent sequences: A174399 A174400 A174401 * A174403 A174404 A174405


KEYWORD

nonn,base


AUTHOR

Harvey P. Dale, Nov 27 2010


STATUS

approved



