A103357 Numbers n such that n and pi(n) (A000720) are palindromic.

1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 22, 33, 262, 323, 393, 525, 535, 555, 666, 818, 878, 949, 2002, 3773, 5775, 6116, 13031, 19591, 39093, 41414, 47374, 59295, 63236, 81918, 94549, 95759, 252252, 394493, 594495, 662266, 674476, 686686, 698896, 764467

Offset

1,2

Links

Giovanni Resta, Table of n, a(n) for n = 1..196 (terms < 10^16)

Formula

a(n) = P_A103358(n).

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; a = {}; Do[p = NextPalindrome[ p]; q = IntegerDigits[ PrimePi[ p]]; If[ Reverse[q] == q, Print[{p, FromDigits[q]}]; AppendTo[a, p]], {n, 10^4}]; a (* Robert G. Wilson v, Feb 03 2005 *)

Crossrefs

Corresponding palindromic pi(n) in A103358.

Cf. A046941, A046942, A103358, A103402, A103403.

Sequence in context: A250412 A201060 A201064 * A055931 A250411 A250410

Adjacent sequences: A103354 A103355 A103356 * A103358 A103359 A103360

Keyword

base,nonn

Author

Zak Seidov, Feb 02 2005

Extensions

More terms from Robert G. Wilson v, Feb 03 2005

Status

approved