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A046942
Numbers k such that k and prime(k) are both palindromes.
7
1, 2, 3, 4, 5, 8114118, 535252535, 4025062605204
OFFSET
1,2
COMMENTS
Previous name: Indices of primes appearing in A046941.
Also, intersection of A002113 and A075807. - Ivan Neretin, Jun 02 2016
LINKS
Eric Weisstein's World of Mathematics, Palindromic Prime.
MATHEMATICA
NextPalindrome[n_] := Block[ {l = Floor[ Log[10, n] + 1], idn = IntegerDigits[n]}, If[ Union[ idn] == {9}, Return[n + 2], If[l < 2, Return[n + 1], If[ FromDigits[ Reverse[ Take[ idn, Ceiling[l/2]]]] FromDigits[ Take[ idn, -Ceiling[l/2]]], FromDigits[ Join[ Take[ idn, Ceiling[l/2]], Reverse[ Take[ idn, Floor[l/2]]] ]], idfhn = FromDigits[ Take[ idn, Ceiling[l/2]]] + 1; idp = FromDigits[ Join[ IntegerDigits[ idfhn], Drop[ Reverse[ IntegerDigits[ idfhn]], Mod[l, 2]]]] ]]]];
p = 0; Do[p = NextPalindrome[p]; While[ !PrimeQ[p], p = NextPalindrome[ p]]; q = IntegerDigits[ PrimePi[ p]]; If[Reverse[q] == q, Print[{p, FromDigits[q]}]], {n, 10^4}] (* Robert G. Wilson v, Feb 03 2005 *)
ParallelDo[If [PalindromeQ @ i && PalindromeQ @ Prime @i, Print @i], {i, 6*10^8}] (* Mikk Heidemaa, May 24 2024 *)
CROSSREFS
Equals pi(A046941).
Sequence in context: A062934 A038106 A347053 * A330929 A307257 A051703
KEYWORD
nice,nonn,base,more
AUTHOR
EXTENSIONS
a(7) from Giovanni Resta, May 14 2003
New name and offset by Ivan Neretin, Jun 02 2016
a(8) from Giovanni Resta, Aug 10 2019
STATUS
approved