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A103403 Palindromic primes q derived from palindromes p such that pi(p) = q. 5
2, 2, 3, 3, 5, 11, 101, 151, 757, 797, 72727, 3485843, 7362637, 753535357, 32792329723 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

From a suggestion from Zak Seidov, Feb 02 2005.

a(16) > pi(32*10^12). [From Donovan Johnson, Dec 03 2009]

LINKS

Table of n, a(n) for n=1..15.

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 = PrimePi[p]; If[PrimeQ[q], r = IntegerDigits[q]; If[Reverse[r] == r, Print[{p, q}]; AppendTo[a, q]]], {n, 10^6}]; a

CROSSREFS

Cf. A046941, A046942, A103357, A103358, A103402.

Sequence in context: A055501 A096010 A102330 * A052473 A165122 A051715

Adjacent sequences:  A103400 A103401 A103402 * A103404 A103405 A103406

KEYWORD

base,nonn

AUTHOR

Robert G. Wilson v, Feb 03 2005

EXTENSIONS

a(15) from Donovan Johnson, Dec 03 2009

STATUS

approved

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Last modified June 19 19:50 EDT 2013. Contains 226416 sequences.