A069469 - OEIS

A069469

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

1, 2, 3, 4, 5, 12, 21, 8114118, 535252535

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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: A109849 A007662 A348370 * A175807 A165303 A109744

Adjacent sequences: A069466 A069467 A069468 * A069470 A069471 A069472

KEYWORD