login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A090840 Smallest prime whose product of digits is 5^n. 5
11, 5, 11551, 15551, 1551551, 15551551, 1155555151, 1555551551, 11555555551, 1155155555551, 555555515551, 555555555551, 5555555555551, 555155555555551, 51555555551555551, 51555555555555551, 1155555555555555551 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Table of n, a(n) for n=0..16.

EXAMPLE

a(4) = 1551551 because its digital product is 5^4.

MATHEMATICA

NextPrim[n_] := Block[{k = n + 1}, While[ !PrimeQ[k], k++ ]; k]; a = Table[0, {18}]; p = 2; Do[q = Log[5, Times @@ IntegerDigits[p]]; If[q != 0 && IntegerQ[q] && a[[q]] == 0, a[[q]] = p; Print[q, " = ", p]]; p = NextPrim[p], {n, 1, 10^9}]

For a(13); a = Map[ FromDigits, Permutations[{1, 1, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5}]]; Min[ Select[a, PrimeQ[ # ] &]]

CROSSREFS

Cf. A089365, A088653, A091465, A090841, A089298.

Sequence in context: A174103 A038319 A002547 * A227775 A204011 A288069

Adjacent sequences:  A090837 A090838 A090839 * A090841 A090842 A090843

KEYWORD

base,nonn

AUTHOR

Robert G. Wilson v, Dec 09 2003

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
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 20 06:56 EDT 2021. Contains 345157 sequences. (Running on oeis4.)