

A124231


Numbers n such that pi(n) is palindromic, where pi(n) is the number of primes less than or equal to n.


1



1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 31, 32, 33, 34, 35, 36, 79, 80, 81, 82, 137, 138, 193, 194, 195, 196, 257, 258, 259, 260, 261, 262
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OFFSET

1,2


LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000


EXAMPLE

Every number from 1 to 28 inclusive belongs to this sequence as the number of primes less than or equal k, which is not more than 28 is a one digit number, which is a palindrome.


MATHEMATICA

Select[Range[300], Reverse[IntegerDigits[PrimePi[ # ]]] == IntegerDigits[PrimePi[ # ]] &]
Position[PrimePi[Range[300]], _?(#==IntegerReverse[#]&)]//Flatten (* The program uses the IntegerReverse function from Mathematica version 10 *) (* Harvey P. Dale, Mar 02 2016 *)


CROSSREFS

Sequence in context: A197640 A246099 A280865 * A154470 A194907 A090106
Adjacent sequences: A124228 A124229 A124230 * A124232 A124233 A124234


KEYWORD

base,nonn


AUTHOR

Tanya Khovanova, Dec 13 2006


STATUS

approved



