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A045548 Numbers n such that final nonzero digit of n! is '4'. 5
4, 7, 20, 21, 23, 25, 26, 28, 37, 42, 49, 52, 55, 56, 58, 64, 69, 75, 76, 78, 87, 92, 99, 100, 101, 103, 112, 117, 124, 134, 135, 136, 138, 140, 141, 143, 147, 152, 155, 156, 158, 164, 169, 179, 182, 195, 196, 198, 202, 205, 206, 208, 214, 219 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

From Robert Israel, Dec 16 2016: (Start)

If n is in the sequence, then:

if n == 0 (mod 5), n+1 is in the sequence;

if n == 1 (mod 5), n+1 is in A045550;

if n == 2 (mod 5), n+1 is in A045547;

if n == 3 (mod 5), n+1 is in A045549. (End)

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

Index entries for sequences related to final digits of numbers

MAPLE

count:= 0:

r:= 1:

for n from 2 while count < 100 do

  r:= r*n;

  if r mod 10 = 0 then r:= r/10^padic:-ordp(r, 5) fi;

  if r mod 10 = 4 then count:= count+1; A[count]:= n fi;

od: seq(A[i], i=1..100); # Robert Israel, Dec 16 2016

MATHEMATICA

f[n_] := Mod[6 Times @@ (Rest[ FoldList[{1 + #1[[1]], #2! 2^(#1[[1]] #2)} &, {0, 0}, Reverse[ IntegerDigits[n, 5]]]]), 10][[2]] (* after Jacob A. Siehler & Greg Dresden in A008904 *); f[0] = f[1] = 1; Select[ Range[150], f[#] == 4 &] (* Robert G. Wilson v, Dec 28 2016 *)

CROSSREFS

Cf. A008904, A045547, A045549, A045550.

Sequence in context: A253208 A275389 A127415 * A090879 A084404 A147065

Adjacent sequences:  A045545 A045546 A045547 * A045549 A045550 A045551

KEYWORD

nonn,base

AUTHOR

Jeff Burch

STATUS

approved

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Last modified February 20 06:26 EST 2019. Contains 320332 sequences. (Running on oeis4.)