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A076449 Least number whose digits can be used to form exactly n different primes (not necessarily using all digits). 6
1, 2, 25, 13, 37, 107, 127, 113, 167, 1027, 179, 137, 1036, 1127, 1013, 1137, 1235, 1136, 1123, 1037, 1139, 1079, 10124, 10126, 1349, 1279, 1237, 3479, 10699, 1367, 10179, 1379, 10127, 10079, 10138, 10123, 10234, 10235, 10247, 10339, 10267 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Smallest m such that A039993(m) = n. - M. F. Hasler, Mar 08 2014

Mike Keith conjectures that a(n) always exists and reports that he has checked this for n <= 66. - N. J. A. Sloane, Jan 25 2008

LINKS

Robert G. Wilson v, Table of n, a(n) for n = 0..457

C. K. Caldwell, The Prime Glossary, Primeval Number

J. P. Delahaye, Primes Hunters, 1379 is very primeval (in French) [broken link]

Mike Keith, Integers containing many embedded primes

W. Schneider, PrimevalNumbers

G. Villemin's Almanach of Numbers, Nombre Primeval de Mike Keith

FORMULA

a(n) = min { m | A039993(m)=n } = min A039993^{-1}(n). - M. F. Hasler, Mar 08 2014

EXAMPLE

a(10) = 179 because 179 is the least number harboring ten primes (namely 7, 17, 19, 71, 79, 97, 179, 197, 719, 971).

MATHEMATICA

(* first do *) Needs["DiscreteMath`Combinatorica`"] (* then *) f[n_] := Length[ Select[ FromDigits /@ Flatten[ Permutations /@ Subsets[ IntegerDigits[ n]], 1], PrimeQ[ # ] &]]; t = Table[0, {50}]; Do[ a = f[n]; If[a < 50 && t[[a + 1]] == 0, t[[a + 1]] = n], {n, 12500}]; t (* Robert G. Wilson v, Feb 12 2005 *)

PROG

(PARI) A076449(n)=for(m=1, 9e9, A039993(m)==n&&return(n)) \\ Not very efficient. - M. F. Hasler, Mar 08 2014

CROSSREFS

Cf. A075053, A072857 gives a similar sequence.

Sequence in context: A249634 A161575 A036502 * A153811 A101962 A092045

Adjacent sequences:  A076446 A076447 A076448 * A076450 A076451 A076452

KEYWORD

base,nonn

AUTHOR

Lekraj Beedassy, Nov 07 2002

EXTENSIONS

Edited by Robert G. Wilson v, Nov 24 2002

Keith link repaired by Charles R Greathouse IV, Aug 13 2009

Definition reworded by M. F. Hasler, Mar 08 2014

a(26) corrected by Robert G. Wilson v, Mar 12 2014

STATUS

approved

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Last modified February 17 21:35 EST 2020. Contains 332006 sequences. (Running on oeis4.)