A178003 Largest n-digit prime with the most digits equal to 5.

5, 59, 557, 5557, 75557, 555557, 9555551, 55555559, 855555559, 5555555557, 75555555557, 555555555559, 5555555555551, 59555555555557, 555555555555557, 6555555555555553, 55556555555555557, 555555555555555559, 9555555555555555551, 85555555555555555559

Offset

1,1

Comments

Select first for the most 5's, then take the largest.

Links

Robert Israel, Table of n, a(n) for n = 1..250

Maple

f:= proc(n) local x, m, xs, sets, s, i, cands;
for m from 1 do
 xs:= subs({seq(i=i+1, i=5..8)}, map(t -> convert(9^m+t, base, 9)[1..m], [$1..9^m-1])):
  sets:= map(t -> t union {1}, combinat:-choose({$2..n}, m-1)):
  cands:=[seq(seq(subsop(seq(s[i]=x[i], i=1..m), [5$n]), s=sets), x=xs)]:
  cands:= sort(map(proc(t) add(t[i]*10^(i-1), i=1..n) end proc, cands), `>`):
  for x in cands do
    if x < 10^(m-1) then break fi;
    if isprime(x) then return x fi
  od:
od:
end proc:
f(1):= 5:
map(f, [$1..20]); # Robert Israel, Nov 25 2025

Crossrefs

Cf. A037063, A105979, A099659

Sequence in context: A385769 A317893 A106105 * A385797 A036947 A099151

Adjacent sequences: A178000 A178001 A178002 * A178004 A178005 A178006

Keyword

nonn,base

Author

Lekraj Beedassy, May 17 2010

Status

approved