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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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified August 24 02:32 EDT 2017. Contains 291052 sequences.