A254449 a(n) is the smallest nonnegative integer such that a(n)! contains a string of exactly n consecutive 4's.

0, 4, 21, 63, 117, 375, 1325, 1253, 5741, 30455, 83393, 68094, 565882, 2666148, 1514639

Offset

0,2

Comments

a(6) and a(7) are anagrams.

Links

Table of n, a(n) for n=0..14.

Example

a(1) = 4 since 4! = 24 contains '4', and 4 is the smallest integer for which this condition is met.
a(2) = 21 since 21! = 51090942171709440000 contains '44'.

Mathematica

A254449[n_] := Module[{m = 0},
   t = Table[4, n];
   While[! MemberQ[Split[IntegerDigits[m!]], t], m++]; m];
Join[{0}, Table[A254449[n], {n, 1, 14}]] (* Robert Price, Mar 20 2019 *)

Prog

(Python)
def A254449(n):
    if n == 0:
        return 0
    i, m, s = 1, 1, '4'*n
    s2 = s+'4'
    while True:
        m *= i
        sn = str(m)
        if s in sn and s2 not in sn:
            return i
        i += 1 # Chai Wah Wu, Dec 29 2015

Crossrefs

Cf. A254042, A254447, A254448, A254500, A254501, A254502, A254716, A254717, A252652.

Sequence in context: A242135 A332981 A135559 * A131478 A089893 A212246

Adjacent sequences: A254446 A254447 A254448 * A254450 A254451 A254452

Keyword

nonn,more,base

Author

Martin Y. Champel, Jan 30 2015

Extensions

a(12) from Jon E. Schoenfield, Feb 27 2015

a(0) prepended by Jon E. Schoenfield, Mar 01 2015

a(14) by Lars Blomberg, Mar 19 2015

a(13) by Bert Dobbelaere, Oct 29 2018

Status

approved