A217407 - OEIS

A217407

Numbers of the form 3^r * 5^s whose decimal representation has a prime number of each digit 0-9.

38171039656829610443115234375, 129892841018736362457275390625, 1766298261467341813095601383375, 83480063729486358039093017578125, 715350795894273434303718560266875, 172661884789704345166683197021484375, 65186341275865666700926353804318984375, 5280093643345119002775034658149837734375

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

This sequence in particular is motivated by the coincidence that both (2^41)*(3^43) and (3^43)*(5^47) have prime numbers of each digit.

LINKS

Robert Israel, Table of n, a(n) for n = 1..11

FORMULA

a(n) = 3^A217408(n) * 5^A217409(n).

EXAMPLE

The first term here is (3^35)*(5^17), corresponding to A217408(1)=35 and A217409(1)=17. Its decimal representation has two each of 0's, 2's, 7's, 8's and 9's; three each of 4's, 5's and 6's; and 5 each of 1's and 3's.

MAPLE

N:= 10^100: # to get all terms <= N

filter:= proc(n) local L, P, d;

L:= convert(n, base, 10);

P:= Vector(10);

for d in L do P[d+1]:= P[d+1]+1 od:

andmap(isprime, P);

end proc:

sort(select(filter, [seq(seq(3^r*5^s, r=0..floor(log[3](N/5^s))), s=0..floor(log[5](N)))])); # Robert Israel, May 08 2017

PROG

(PARI) prDigits(n)=my(d=digits(n), v=vector(10)); for(i=1, #d, v[d[i]+1]++); for(i=1, 10, if(!isprime(v[i]), return(0))); 1

list(lim)=my(v=List(), t); for(a=0, log(lim+.5)\log(5), t=5^a; while(t<=lim, if(prDigits(t), listput(v, t)); t*=3)); vecsort(Vec(v)) \\ Charles R Greathouse IV, Sep 19 2013

CROSSREFS

Subsequence of A215876.

Cf. A216854, A217408, A217409, A217404, A217410, A217413, A217416, A217419, A217422, A217425, A217428, A217431.

Sequence in context: A105301 A104300 A095450 * A280350 A095452 A068214

Adjacent sequences: A217404 A217405 A217406 * A217408 A217409 A217410

KEYWORD

nonn,base,less

AUTHOR

James G. Merickel, Oct 02 2012

EXTENSIONS

More terms from Robert Israel, May 08 2017

STATUS

approved