A047814 Largest prime substring of n, or 0 if no such substring exists.

0, 0, 2, 3, 0, 5, 0, 7, 0, 0, 0, 11, 2, 13, 0, 5, 0, 17, 0, 19, 2, 2, 2, 23, 2, 5, 2, 7, 2, 29, 3, 31, 3, 3, 3, 5, 3, 37, 3, 3, 0, 41, 2, 43, 0, 5, 0, 47, 0, 0, 5, 5, 5, 53, 5, 5, 5, 7, 5, 59, 0, 61, 2, 3, 0, 5, 0, 67, 0, 0, 7, 71, 7, 73, 7, 7, 7, 7, 7, 79, 0, 0, 2, 83, 0, 5, 0, 7, 0, 89

Offset

0,3

Comments

A211396(n) <= a(n). - Reinhard Zumkeller, Feb 08 2013

Links

Reinhard Zumkeller, Table of n, a(n) for n = 0..10000

Example

a(10)=0, a(1227)=227.

Mathematica

a[n_] := (id = IntegerDigits[n]; lg = Length[id]; sel = Select[ FromDigits /@ Flatten[ Table[ id[[i ;; j]], {i, 1, lg}, {j, i, lg}], 1], PrimeQ]; If[ sel === {}, 0, Last[ Sort[ sel] ] ]); Table[ a[n], {n, 0, 99}] (* Jean-François Alcover, Feb 23 2012 *)
lps[m_]:=Max[Select[Flatten[Table[FromDigits/@Partition[ IntegerDigits[ m], n, 1], {n, IntegerLength[m]}]], PrimeQ]]; Array[lps, 100, 0]/. -\[Infinity]->0 (* Harvey P. Dale, Feb 26 2014 *)

Prog

(Haskell)
import Data.List (isInfixOf)
a047814 n = if null ips then 0 else head ips
   where ips = [p | p <- reverse $ takeWhile (<= n) a000040_list,
                    show p `isInfixOf` show n]
-- Reinhard Zumkeller, Feb 08 2013

Crossrefs

Cf. A211396.

Sequence in context: A093438 A211396 A331097 * A365276 A101991 A296065

Adjacent sequences: A047811 A047812 A047813 * A047815 A047816 A047817

Keyword

nonn,easy,base,nice,look

Author

N. J. A. Sloane

Extensions

Corrected (41) by Jean-François Alcover, Feb 23 2012

Status

approved