

A100415


Numbers n such that n is R(n)th nonprime number, where R(n) is the digit reversal of n (A018252(A004086(n))=n).


2



1, 64, 524, 534, 58725, 907538, 6264385, 9438088, 9596598, 27895162, 422984004, 548911025, 8804661048, 49640253574, 63899981216, 95138721219, 97895906839, 469449672154
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OFFSET

1,2


COMMENTS

n is in the sequence iff n is not prime and R(n)=npi(n). There is no further term up to 3670000000.
a(19) > 10^13. Up to that limit, this sequence contains all the numbers k such that R(k) = k  pi(k).  Giovanni Resta, Aug 08 2019


LINKS

Table of n, a(n) for n=1..18.


EXAMPLE

548911025 is in the sequence because 548911025 is the 520118945th nonprime natural number.


MATHEMATICA

Do[s = FromDigits[Reverse[IntegerDigits[n]]]; If[ ! PrimeQ[n] && s == n  PrimePi[n], Print[n]], {n, 548911025}]


CROSSREFS

Cf. A018252, A004086, A100413, A100414, A114926.
Sequence in context: A016803 A066430 A115740 * A200841 A247929 A070054
Adjacent sequences: A100412 A100413 A100414 * A100416 A100417 A100418


KEYWORD

nonn,base,more


AUTHOR

Farideh Firoozbakht, Dec 12 2004


EXTENSIONS

a(13)a(18) from Giovanni Resta, Aug 08 2019


STATUS

approved



