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A124231 Numbers k such that pi(k) is palindromic, where pi(k) is the number of primes less than or equal to k. 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
EXAMPLE
Every number from 1 to 28 inclusive belongs to this sequence as the number of primes less than or equal to k, for k <= 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 * A352800 A154470 A194907
KEYWORD
base,nonn
AUTHOR
Tanya Khovanova, Dec 13 2006
STATUS
approved

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Last modified March 19 07:21 EDT 2024. Contains 370955 sequences. (Running on oeis4.)