

A069469


Numbers n such that prime(reversal(n)) = reversal(prime(n)). Ignore leading 0's.


1




OFFSET

1,2


COMMENTS

For an arithmetical function f, call the arguments n such that f(reverse(n)) = reverse(f(n)) the "palinpoints" of f. This sequence is the sequence of palinpoints of f(n) = prime(n).
These are all the palinpoints of prime(n) not exceeding 10^7. There are more (535252535 is known to be a term, but it is not known whether it is the next one).
Contains all n such that n and prime(n) are both palindromes, i.e. A046942. Heuristically, we would expect there to be infinitely many of these, but they will be rare: the number of them with at most d digits may be on the order of sqrt(d).  Robert Israel, May 30 2016
a(10) > 10^9.  Giovanni Resta, Apr 13 2017


LINKS

Table of n, a(n) for n=1..9.


EXAMPLE

Let f(n) = Prime(n). Then f(21) = 73, f(12) = 37, so f(reverse(21)) = reverse(f(21)). Therefore 21 belongs to the sequence.


MATHEMATICA

rev[n_] := FromDigits[Reverse[IntegerDigits[n]]]; f[n_] := Prime[n]; Select[Range[10^5], f[rev[ # ]] == rev[f[ # ]] &]


CROSSREFS

Cf. A000040, A002113, A075807, A046942.
Sequence in context: A117577 A109849 A007662 * A175807 A165303 A109744
Adjacent sequences: A069466 A069467 A069468 * A069470 A069471 A069472


KEYWORD

base,nonn


AUTHOR

Joseph L. Pe, Apr 15 2002


EXTENSIONS

a(8) added by Ivan Neretin, May 30 2016
a(9) from Giovanni Resta, Apr 13 2017


STATUS

approved



