login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A046942 Numbers n such that n and prime(n) are both palindromes. 7
1, 2, 3, 4, 5, 8114118, 535252535 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Previous name: Indices of primes appearing in A046941.

Also, intersection of A002113 and A075807. - Ivan Neretin, Jun 02 2016

LINKS

Table of n, a(n) for n=1..7.

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 *)

CROSSREFS

Equals pi(A046941).

Cf. A046941, A103357, A103358, A103402, A103403.

Sequence in context: A004911 A062934 A038106 * A051703 A004567 A030378

Adjacent sequences:  A046939 A046940 A046941 * A046943 A046944 A046945

KEYWORD

nice,nonn,base

AUTHOR

Carlos Rivera

EXTENSIONS

a(7) from Giovanni Resta, May 14 2003

New name and offset by Ivan Neretin, Jun 02 2016

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified October 20 23:11 EDT 2017. Contains 293679 sequences.