A049782 -id:A049782 - cp's OEIS frontend

A003422 Left factorials: !n = Sum_{k=0..n-1} k!.

0, 1, 2, 4, 10, 34, 154, 874, 5914, 46234, 409114, 4037914, 43954714, 522956314, 6749977114, 93928268314, 1401602636314, 22324392524314, 378011820620314, 6780385526348314, 128425485935180314, 2561327494111820314, 53652269665821260314, 1177652997443428940314

Offset: 0

N. J. A. Sloane, R. K. Guy

Number of {12, 12*, 1*2, 21*}- and {12, 12*, 21, 21*}-avoiding signed permutations in the hyperoctahedral group.
a(n) is the number of permutations on [n] that avoid the patterns 2n1 and n12. An occurrence of a 2n1 pattern is a (scattered) subsequence a-n-b with a > b. - David Callan, Nov 29 2007
Also, numbers left over after the following sieving process: At step 1, keep all numbers of the set N = {0, 1, 2, ...}. In step 2, keep only every second number after a(2) = 2: N' = {0, 1, 2, 4, 6, 8, 10, ...}. In step 3, keep every third of the numbers following a(3) = 4, N" = {0, 1, 2, 4, 10, 16, 22, ...}. In step 4, keep every fourth of the numbers beyond a(4) = 10: {0, 1, 2, 4, 10, 34, 58, ...}, and so on. - M. F. Hasler, Oct 28 2010
If s(n) is a second-order recurrence defined as s(0) = x, s(1) = y, s(n) = n*(s(n - 1) - s(n - 2)), n > 1, then s(n) = n*y - n*a(n - 1)*x. - Gary Detlefs, May 27 2012
a(n) is the number of lists of {1, ..., n} with (1st element) = (smallest element) and (k-th element) <> (k-th smallest element) for k > 1, where a list means an ordered subset. a(4) = 10 because we have the lists: [1], [2], [3], [4], [1, 3, 2], [1, 4, 2], [1, 4, 3], [2, 4, 3], [1, 3, 4, 2], [1, 4, 2, 3]. Cf. A000262. - Geoffrey Critzer, Oct 04 2012
Consider a tree graph with 1 vertex. Add an edge to it with another vertex. Now add 2 edges with vertices to this vertex, and then 3 edges to each open vertex of the tree (not the first one!), and the next stage is to add 4 edges, and so on. The total number of vertices at each stage give this sequence (see example). - Jon Perry, Jan 27 2013
Additive version of the superfactorials A000178. - Jon Perry, Feb 09 2013
Repunits in the factorial number system (see links). - Jon Perry, Feb 17 2013
Whether n|a(n) only for 1 and 2 remains an open problem. A published 2004 proof was retracted in 2011. This is sometimes known as Kurepa's conjecture. - Robert G. Wilson v, Jun 15 2013, corrected by Jeppe Stig Nielsen, Nov 07 2015.
!n is not always squarefree for n > 3. Miodrag Zivkovic found that 54503^2 divides !26541. - Arkadiusz Wesolowski, Nov 20 2013
a(n) gives the position of A007489(n) in A227157. - Antti Karttunen, Nov 29 2013
Matches the total domination number of the Bruhat graph from n = 2 to at least n = 5. - Eric W. Weisstein, Jan 11 2019
For the connection with Kurepa trees, see A. Petojevic, The {K_i(z)}{i=1..oo} functions, Rocky Mtn. J. Math., 36 (2006), 1637-1650. - _Aleksandar Petojevic, Jun 29 2018
This sequence converges in the p-adic topology, for every prime number p. - Harry Richman, Aug 13 2024

			!5 = 0! + 1! + 2! + 3! + 4! = 1 + 1 + 2 + 6 + 24 = 34.
x + 2*x^2 + 4*x^3 + 10*x^4 + 34*x^5 + 154*x^6 + 874*x^7 + 5914*x^8 + 46234*x^9 + ...
From _Arkadiusz Wesolowski_, Aug 06 2012: (Start)
Illustration of initial terms:
.
. o        o         o            o                         o
.          o         o            o                         o
.                   o o          o o                       o o
.                              ooo ooo                   ooo ooo
.                                             oooo oooo oooo oooo oooo oooo
.
. 1        2         4            10                        34
.
(End)
The tree graph. The total number of vertices at each stage is 1, 2, 4, 10, ...
    0 0
    |/
    0-0
   /
0-0
   \
    0-0
    |\
    0 0
- _Jon Perry_, Jan 27 2013

Richard K. Guy, Unsolved Problems Number Theory, Section B44.
D. Kurepa, On the left factorial function !n. Math. Balkanica 1 1971 147-153.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

T. D. Noe, Table of n, a(n) for n = 0..100
P. J. Cameron, Sequences realized by oligomorphic permutation groups, J. Integ. Seqs. Vol. 3 (2000), Article 00.1.5.
Bernd C. Kellner, Some remarks on Kurepa's left factorial, arXiv:math/0410477 [math.NT], 2004.
D. Kurepa, On the left factorial function !N, Math. Balkanica 1 (1971), 147-153. (Annotated scanned copy).
T. Mansour and J. West, Avoiding 2-letter signed patterns, arXiv:math/0207204 [math.CO], 2002.
Romeo Meštrović, Variations of Kurepa's left factorial hypothesis, arXiv preprint arXiv:1312.7037 [math.NT], 2013.
Romeo Meštrović, The Kurepa-Vandermonde matrices arising from Kurepa's left factorial hypothesis, Filomat 29:10 (2015), 2207-2215; DOI 10.2298/FIL1510207M.
Hisanori Mishima, Factorizations of many number sequences.
Hisanori Mishima, Factorizations of many number sequences
F. J. Papp, Letter to N. J. A. Sloane, Nov 1974.
Jon Perry, Sum of Factorials. [Broken link?]
Aleksandar Petojevic, On Kurepa's hypothesis for the left factorial, Filomat, Vol. 12, No. 1, 1998.
Alexsandar Petojevic, The Function vM_m(s; a; z) and Some Well-Known Sequences, Journal of Integer Sequences, Vol. 5 (2002), Article 02.1.7.
Aleksandar Petojevic, The {K_i(z)}_{i=1..oo} functions, Rocky Mtn. J. Math., 36 (2006), 1637-1650.
Aleksandar Petojević, Marjana Gorjanac Ranitović, Dragan Rastovac, and Milinko Mandić, The Golden Ratio, Factorials, and the Lambert W Function, Journal of Integer Sequences, Vol. 27 (2024), Article 24.5.7.
Eric Weisstein's World of Mathematics, Factorial Sums.
Eric Weisstein's World of Mathematics, Left Factorial.
Eric Weisstein's World of Mathematics, Repunit.
Wikipedia, Factorial number system.
Miodrag Zivkovic, The number of primes sum_{i=1..n} (-1)^(n-i)*i! is finite, Math. Comp. 68 (1999), pp. 403-409.
Index entries for sequences related to factorial numbers.

Equals A007489(n-1)+1 for n>=1. Cf. A000142, A014144, A005165.
Twice A014288. See also A049782, A100612.
Cf. A102639, A102411, A102412, A101752, A094216, A094638, A008276, A000166, A000110, A000204, A000045, A000108, A135722, A227157, A000178, A137338, A232845, A357145.

a003422 n = a003422_list !! n
a003422_list = scanl (+) 0 a000142_list
-- Reinhard Zumkeller, Dec 27 2011

A003422 := proc(n) local k; add(k!,k=0..n-1); end proc:
# Alternative, using the Charlier polynomials A137338:
C := proc(n, x) option remember; if n > 0 then (x-n)*C(n-1, x) - n*C(n-2, x)
elif n = 0 then 1 else 0 fi end: A003422 := n -> (-1)^(n+1)*C(n-1, -1):
seq(A003422(n), n=0..22); # Peter Luschny, Nov 28 2018
# third Maple program:
a:= proc(n) option remember; `if`(n=0, 0, a(n-1)+(n-1)!) end:
seq(a(n), n=0..23);  # Alois P. Heinz, Feb 24 2022

Table[Sum[i!, {i, 0, n - 1}], {n, 0, 20}] (* Stefan Steinerberger, Mar 31 2006 *)
Join[{0}, Accumulate[Range[0, 25]!]] (* Harvey P. Dale, Nov 19 2011 *)
a[0] = 0; a[1] = 1; a[n_] := a[n] = n*a[n - 1] - (n - 1)*a[n - 2]; Array[a, 23, 0] (* Robert G. Wilson v, Jun 15 2013 *)
a[n_] := (-1)^n*n!*Subfactorial[-n-1]-Subfactorial[-1]; Table[a[n] // FullSimplify, {n, 0, 22}] (* Jean-François Alcover, Jan 09 2014 *)
RecurrenceTable[{a[n] == n a[n - 1] - (n - 1) a[n - 2], a[0] == 0, a[1] == 1}, a, {n, 0, 10}] (* Eric W. Weisstein, Jan 11 2019 *)
Range[0, 20]! CoefficientList[Series[(ExpIntegralEi[1] - ExpIntegralEi[1 - x]) Exp[x - 1], {x, 0, 20}], x] (* Eric W. Weisstein, Jan 11 2019 *)
Table[(-1)^n n! Subfactorial[-n - 1] - Subfactorial[-1], {n, 0, 20}] // FullSimplify (* Eric W. Weisstein, Jan 11 2019 *)
Table[(I Pi + ExpIntegralEi[1] + (-1)^n n! Gamma[-n, -1])/E, {n, 0, 20}] // FullSimplify (* Eric W. Weisstein, Jan 11 2019 *)

makelist(sum(k!,k,0,n-1), n, 0, 20); /* Stefano Spezia, Jan 11 2019 */

a003422(n)=sum(k=0,n-1,k!) \\ Charles R Greathouse IV, Jun 15 2011

from itertools import count, islice
def A003422_gen(): # generator of terms
    yield from (0,1)
    c, f = 1, 1
    for n in count(1):
        yield (c:= c + (f:= f*n))
A003422_list = list(islice(A003422_gen(),20)) # Chai Wah Wu, Jun 22 2022

def a(n):
    if n == 0: return 0
    s = f = 1
    for k in range(1, n):
        f *= k
        s += f
    return round(s)
print([a(n) for n in range(24)])  # Peter Luschny, Mar 05 2024

D-finite with recurrence: a(n) = n*a(n - 1) - (n - 1)*a(n - 2). - Henry Bottomley, Feb 28 2001
Sequence is given by 1 + 1*(1 + 2*(1 + 3*(1 + 4*(1 + ..., terminating in n*(1)...). - Jon Perry, Jun 01 2004
a(n) = Sum_{k=0..n-1} P(n, k) / C(n, k). - Ross La Haye, Sep 20 2004
E.g.f.: (Ei(1) - Ei(1 - x))*exp(-1 + x) where Ei(x) is the exponential integral. - Djurdje Cvijovic and Aleksandar Petojevic, Apr 11 2000
a(n) = Integral_{x = 0..oo} [(x^n - 1)/(x - 1)]*exp(-x) dx. - Gerald McGarvey, Oct 12 2007
A007489(n) = !(n + 1) - 1 = a(n + 1) - 1. - Artur Jasinski, Nov 08 2007. Typos corrected by Antti Karttunen, Nov 29 2013
Starting (1, 2, 4, 10, 34, 154, ...), = row sums of triangle A135722. - Gary W. Adamson, Nov 25 2007
a(n) = a(n - 1) + (n - 1)! for n >= 2. - Jaroslav Krizek, Jun 16 2009
E.g.f. A(x) satisfies the differential equation A'(x) = A(x) + 1/(1 - x). - Vladimir Kruchinin, Jan 19 2011
a(n + 1) = p(-1) where p(x) is the unique degree-n polynomial such that p(k) = A182386(k) for k = 0, 1, ..., n. - Michael Somos, Apr 27 2012
From Sergei N. Gladkovskii, May 09 2013 to Oct 22 2013: (Start)
Continued fractions:
G.f.: x/(1-x)*Q(0) where Q(k) = 1 + (2*k + 1)*x/( 1 - 2*x*(k+1)/(2*x*(k+1) + 1/Q(k+1))).
G.f.: G(0)*x/(1-x)/2 where G(k) = 1 + 1/(1 - x*(k+1)/(x*(k+1) + 1/G(k+1))).
G.f.: 2*x/(1-x)/G(0) where G(k) = 1 + 1/(1 - 1/(1 - 1/(2*x*(k+1)) + 1/G(k+1))).
G.f.: W(0)*x/(1+sqrt(x))/(1-x) where W(k) = 1 + sqrt(x)/(1 - sqrt(x)*(k+1)/(sqrt(x)*(k+1) + 1/W(k+1))).
G.f.: B(x)*(1+x)/(1-x) where B(x) is the g.f. of A153229.
G.f.: x/(1-x) + x^2/(1-x)/Q(0) where Q(k) = 1 - 2*x*(2*k+1) - x^2*(2*k+1)*(2*k+2)/(1 - 2*x*(2*k+2) - x^2*(2*k+2)*(2*k+3)/Q(k+1)).
G.f.: x*(1+x)*B(x) where B(x) is the g.f. of A136580. (End)
a(n) = (-1)^(n+1)*C(n-1, -1) where C(n, x) are the Charlier polynomials (with parameter a=1) as given in A137338. (Evaluation at x = 1 gives A232845.) - Peter Luschny, Nov 28 2018
a(n) = (a(n-3)*(n-2)^2*(n-3)! + a(n-1)^2)/a(n-2) (empirical). - Gary Detlefs, Feb 25 2022
a(n) = signum(n)/b(1,n) with b(i,n) = i - [iMohammed Bouras, Sep 07 2022
Sum_{n>=1} 1/a(n) = A357145. - Amiram Eldar, Oct 01 2022

A061062 Sum of squared factorials: (0!)^2 + (1!)^2 + (2!)^2 + (3!)^2 +...+ (n!)^2.

Original entry on oeis.org

1, 2, 6, 42, 618, 15018, 533418, 25935018, 1651637418, 133333531818, 13301522971818, 1606652445211818, 231049185247771818, 39006837228880411818, 7639061293780877851818, 1717651314017980301851818

Offset: 0

Jason Earls, May 27 2001

nonn

There is a Kurepa-like conjecture (see A049782) for this sequence: for primes p>3, p does not divide a(p-1). However, the conjecture fails for p=20879. - T. D. Noe, Dec 08 2004

			a(2) = 0!*0! + 1!*1! + 2!*2! = 6.

Seiichi Manyama, Table of n, a(n) for n = 0..253 (terms 0..100 from Harry J. Smith)

Cf. A001044, A100288 (primes of the form (1!)^2 + (2!)^2 + (3!)^2 +...+ (k!)^2), A104344 (if sum starts at k=1), A049782.

A061062:=n->sum((k!)^2, k=0..n): seq(A061062(n), n=0..15); # Zerinvary Lajos, Jan 22 2008

s=0; Table[s=s+(n!)^2, {n, 0, 20}]
Accumulate[(Range[0,20]!)^2] (* Harvey P. Dale, Apr 19 2015 *)

{ a=0; for (n=0, 100, write("b061062.txt", n, " ", a+=(n!)^2) ) } \\ Harry J. Smith, Jul 17 2009

a(n) = sum(k=0...n, (n-k)!^2 ). - Ross La Haye, Sep 21 2004

Recurrence: a(0) = 1, a(1) = 2, a(n) = (n^2+1)*a(n-1) - n^2*a(n-2). - Vladimir Reshetnikov, Oct 28 2015

More terms from T. D. Noe, Dec 08 2004

A057245 Numbers m such that m | Sum_{k=1..m} k!.

Original entry on oeis.org

1, 3, 9, 11, 33, 99

Offset: 1

Robert G. Wilson v, Sep 21 2000

n such that A067462(n) = 0. - T. D. Noe, May 13 2010
For any terms in this sequence, their LCM also belongs to this sequence. Term a(7), if it exists, is prime. - Max Alekseyev, Oct 14 2012
n > 1 is in this sequence iff A049782(n) = 1. - Max Alekseyev, Apr 17 2016
If it exists, a(7) > 12000000. - Bert Dobbelaere, Oct 28 2018
If it exists, a(7) > 1.6*10^8. - Giovanni Resta, Nov 09 2018

Richard K. Guy, Unsolved Problems in Number Theory, Springer, Third Ed., 2004, Section B44.

Cf. A007489, A049782, A064383.

Filtered([1..1500],m->Sum([1..m],k->Factorial(k)) mod m = 0); # Muniru A Asiru, Oct 28 2018

a = 0; b = 1; k = 2; While[k < 250001, c = k*b - (k - 1) a;
If[ Mod[c, k] == 1, Print[k]]; a = b; b = c; k++] (* Robert G. Wilson v, Jun 15 2013 *)

A100612 a(n) = (0! + 1! + ... + (p-1)!) mod p, where p = prime(n).

Original entry on oeis.org

0, 1, 4, 6, 1, 10, 13, 9, 21, 17, 2, 5, 4, 16, 18, 13, 28, 22, 65, 68, 55, 20, 27, 76, 80, 13, 50, 43, 65, 109, 56, 81, 93, 134, 82, 10, 131, 4, 30, 104, 29, 170, 104, 165, 9, 122, 130, 42, 225, 50, 69, 12, 128, 60, 147, 52, 16, 56, 7, 218, 154, 264, 198, 48, 299, 205, 251, 101

Offset: 1

N. J. A. Sloane, Dec 02 2004

nonn

The greedy inverse (indices of first occurrence of 1, 2, 3, ... in the sequence) is 2, 11, 91, 3, 12, 4, 59, -1, 8, 6, -1, 52, 7, 2550, -1, 14, 10, 15, 5461, 22, 9, 18, 205, 141, 4178, -1, 23, 17, 41, 39, -1, 5297, 937, -1, -1, -1, -1, 5248, 213, -1, 90, 48, 28, 4202, -1, 1718, 313, 64, 119, 27, ... where -1 means the number does not exist or is larger than 8000. - R. J. Mathar, Dec 19 2016
a(12397) = 31; a(54708) = 37. - Michel Marcus, May 11 2019
a(105527) = 35. - Michel Marcus, May 13 2019
a(16728884) = 26; a(62860131) = 35; sent by Milos Tatarevic. - Michel Marcus, May 18 2019

R. K. Guy, Unsolved Problems in Number Theory, B44: is a(n)>0 for n>2?

Michel Marcus, Table of n, a(n) for n = 1..2000
Vladica Andrejic and Milos Tatarevic, Searching for a counterexample to Kurepa's Conjecture, arXiv:1409.0800 [math.NT], 2014-2015.
Vladica Andrejic, Alin Bostan, Milos Tatarevic, Improved algorithms for left factorial residues, arXiv:1904.09196 [math.NT], 2019.
Luis H. Gallardo, Artin-Schreier, Erdős, and Kurepa’s conjecture, 2023.
Romeo Mestrovic, Variations of Kurepa's left factorial hypothesis, arXiv preprint arXiv:1312.7037 [math.NT], 2013-2014.
T. D. Noe, Plot of first 5000 terms (The red line gives prime(n). There are very few duplicate values in the sequence; the 5000 terms have 4476 values.)

See A049782 for more information. See also A003422, A236399.

Cf. A067462.

lf:=n->add(k!,k=0..n-1);
[seq(lf(ithprime(n)) mod ithprime(n),n=1..100)];
# 2nd program:
A100612 := proc(n)
    local p,f,a,k;
    f := 1 ;
    a := 0 ;
    p := ithprime(n) ;
    for k from 0 to p-1 do
        a := modp(a+f,p) ;
        f := modp(f*(k+1),p) ;
    end do:
    a ;
end proc:
seq(A100612(n),n=1..50) ; # R. J. Mathar, Dec 19 2016

Table[Mod[Total[Range[0,n-1]!],n],{n,Prime[Range[70]]}] (* Harvey P. Dale, May 06 2013 *)

a(n) = {my(p = prime(n), v = vector(p-1, k, Mod(k, p))); for (k=2, p-1, v[k] *= v[k-1];); lift(1+vecsum(v));} \\ Michel Marcus, May 05 2019

a(n) = A236399(n) mod prime(n).

a(n) = A067462(prime(n)) + 1, unless A067462(prime(n)) == - 1 (mod n). - Michel Marcus, May 05 2019

A067462 a(n) = (1! + 2! + ... + (n-1)!) mod n.

Original entry on oeis.org

0, 1, 0, 1, 3, 3, 5, 1, 0, 3, 0, 9, 9, 5, 3, 9, 12, 9, 8, 13, 12, 11, 20, 9, 13, 9, 9, 5, 16, 3, 1, 25, 0, 29, 33, 9, 4, 27, 9, 33, 3, 33, 15, 33, 18, 43, 17, 9, 47, 13, 12, 9, 12, 9, 33, 33, 27, 45, 27, 33, 21, 1, 54, 25, 48, 33, 64, 29, 66, 33, 67, 9, 54, 41, 63, 65, 33, 9, 19, 73, 63

Offset: 1

Alex Fink, Feb 24 2002

A.H.M. Smeets, Table of n, a(n) for n = 1..20000 (first 1000 terms from T. D. Noe)

Cf. A049782.

Mod[ #[[1]], #[[2]]]&/@Transpose[{Rest[FoldList[Plus, 0, Factorial[Range[90]]]], Range[90]}]
Table[Mod[Total[Range[n-1]!],n],{n,90}] (* Harvey P. Dale, Jan 23 2023 *)

a(n) = my(s=0, p=1); for (i=1, n-1, f = Mod(i, n); p*=f; s += p); lift(s); \\ Michel Marcus, Aug 19 2019

n = 0
while n < 200:
    n,f,fs,i = n+1,1,0,1
    while i < n:
        f,i = (f*i)%n,i+1
        fs = (fs+f)%n
    print(n,fs) # A.H.M. Smeets, Aug 19 2019

A176787 a(n) = (0!-1!+2!-3!....(-1)^(n-1)*(n-1)!) mod n.

Original entry on oeis.org

0, 0, 2, 0, 0, 2, 4, 4, 8, 0, 5, 8, 0, 4, 5, 12, 9, 8, 15, 0, 11, 16, 19, 20, 20, 0, 17, 4, 20, 20, 10, 28, 5, 26, 25, 8, 0, 34, 26, 20, 2, 32, 6, 16, 35, 42, 7, 44, 11, 20, 26, 0, 21, 44, 5, 4, 53, 20, 33, 20, 49, 10, 53, 60, 0, 38, 6, 60, 65, 60, 65, 44, 16, 0, 20, 72, 60, 26, 5, 60, 17

Offset: 1

Paolo P. Lava & Giorgio Balzarotti, Apr 26 2010

nonn

			a(1) = 0! mod 1 = 1 mod 1 = 0;
a(2) = (0!-1!) mod 2 = (1 - 1) mod 2 = 0;
a(3) = (0!-1!+2!) mod 3 = (1 - 1 + 2) mod 3 = 2.

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Cf. A049782, A064383 (n such that a(n) is 0).

A176787 := proc(n): add((-1)^(k-1)*(k-1)!, k=1..n) mod n end: seq(A176787(n),n=1..81); # Johannes W. Meijer, Jun 28 2011

Table[Mod[Sum[(-1)^k*k!, {k, 0, n - 1}], n], {n, 81}] (* Michael De Vlieger, Apr 22 2015 *)

a(n) = sum(k=0, n-1, (-1)^k*k!) % n; \\ Michel Marcus, Apr 22 2015

a(n) = A058006(n) mod n. - R. J. Mathar, Jul 13 2012

Edited by Johannes W. Meijer, Jun 28 2011

A176788 a(n) = (0!! + 1!! + 2!! + 3!! + ... + (n-1)!!) mod n.

Original entry on oeis.org

0, 0, 1, 3, 0, 0, 1, 7, 0, 2, 6, 3, 12, 10, 12, 3, 13, 6, 11, 7, 3, 8, 14, 15, 12, 22, 15, 3, 19, 12, 16, 11, 30, 14, 17, 15, 17, 34, 9, 7, 26, 24, 36, 19, 42, 8, 2, 3, 24, 12, 48, 35, 2, 42, 52, 31, 15, 22, 51, 27, 32, 56, 24, 27, 22, 30, 6, 31, 54, 52, 12, 15, 7, 56, 12, 15, 52, 48

Offset: 1

Paolo P. Lava & Giorgio Balzarotti, Apr 26 2010

			0!! mod 1 = 1 mod 1 = 0.
(0!!+1!!) mod 2 = (1 + 1) mod 2 = 0.
(0!!+1!!+2!!) mod 3 = (1 + 1 + 2) mod 3 = 1.

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Cf. A049782, A176787, A176789.

A176788 := proc(n)
        A129981(n-1) mod n ;
end proc: # R. J. Mathar, Jul 13 2012

Table[Mod[Total[Range[0,n-1]!!],n],{n,80}] (* Harvey P. Dale, Nov 15 2021 *)

a(n) = A129981(n-1) mod n.

A176789 a(n) = (0!! - 1!! + 2!! - 3!! + ... + (-1)^(n-1)*(n-1)!!) mod n.

Original entry on oeis.org

0, 0, 2, 3, 2, 4, 5, 7, 4, 4, 2, 7, 3, 0, 4, 3, 5, 10, 3, 19, 7, 4, 3, 7, 14, 0, 10, 7, 5, 4, 29, 11, 4, 6, 14, 19, 4, 26, 13, 39, 13, 28, 2, 15, 19, 20, 11, 19, 14, 14, 40, 39, 0, 10, 4, 7, 7, 8, 7, 19, 26, 38, 28, 27, 39, 4, 57, 23, 43, 14, 5, 55, 30, 6, 64, 7, 70, 52, 50, 19, 37, 10, 75, 7

Offset: 1

Paolo P. Lava & Giorgio Balzarotti, Apr 26 2010

Alternating sum of double factorials modulo n.

			a(1) = 0!! mod 1 = 1 mod 1 = 0.
a(2) = (0!! - 1!!) mod 2 = (1 - 1) mod 2 = 0.
a(3) = (0!! - 1!! + 2!!) mod 3 = (1 - 1 + 2) mod 3 = 2.

Cf. A049782, A176787, A176788.

A176789 := proc(n)
        modp(1-(-1)^n*A129831(n-1), n) ;
end proc: # R. J. Mathar, Aug 22 2012

Table[Mod[Sum[(-1)^k k!!,{k,0,n-1}],n],{n,90}] (* Harvey P. Dale, Dec 08 2012 *)

a(n) = (Sum_{k=0..n-1} (-1)^k*k!!) mod n = (1 + (-1)^(n-1)*A129831(n-1)) mod n.

A258944 Odd primes p that divide 2! + 3! + ... + (p-1)!.

Original entry on oeis.org

31, 373, 6855730873

Offset: 1

Jeppe Stig Nielsen, Nov 07 2015

In other words, the odd primes p that divide A003422(p) - 2. Or the primes p with A049782(p) = 2.

Andrejic and Tatarevic found a(3).

Vladica Andrejic and Milos Tatarevic, Searching for a counterexample of Kurepa's Conjecture, arXiv:1409.0800 [math.NT], 2014.

Cf. A003422, A049782, A100612.

forprime(p=3, 1e11, if(sum(k=2, p-1, k!) % p==0, print1(p, ", "))); \\ Altug Alkan, Nov 08 2015

cp's OEIS Frontend

A003422 Left factorials: !n = Sum_{k=0..n-1} k!.

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A061062 Sum of squared factorials: (0!)^2 + (1!)^2 + (2!)^2 + (3!)^2 +...+ (n!)^2.

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A057245 Numbers m such that m | Sum_{k=1..m} k!.

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A100612 a(n) = (0! + 1! + ... + (p-1)!) mod p, where p = prime(n).

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A067462 a(n) = (1! + 2! + ... + (n-1)!) mod n.

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A176787 a(n) = (0!-1!+2!-3!....(-1)^(n-1)*(n-1)!) mod n.

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A176788 a(n) = (0!! + 1!! + 2!! + 3!! + ... + (n-1)!!) mod n.