A062795 Duplicate of A062363.
0, 1, 3, 7, 27, 121, 729, 5041, 40347, 362887, 3628923, 39916801, 479002353
Offset: 0
This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
G.f.: A(x) = 1 + x + 2*x^2 + 4*x^3 + 11*x^4 + 37*x^5 + 167*x^6 +... A(x) = 1/((1-x)*(1-x^2)*(1-x^3)^2*(1-x^4)^6*(1-x^5)^24*(1-x^6)^120*...). log(A(x)) = x + 3*x^2/2 + 7*x^3/3 + 27*x^4/4 + 121*x^5/5 + 729*x^6/6 + 5041*x^7/7 + 40347*x^8/8 +...+ A062363(n)*x^n/n +...
b:= proc(n, i) option remember; `if`(n=0, 1, `if`(i<1, 0, add(b(n-i*j, i-1)*binomial((i-1)!+j-1, j), j=0..n/i))) end: a:= n-> b(n$2): seq(a(n), n=0..23); # Alois P. Heinz, Aug 10 2021
nmax=20; CoefficientList[Series[Product[1/(1-x^k)^((k-1)!),{k,1,nmax}],{x,0,nmax}],x] (* Vaclav Kotesovec, Mar 14 2015 *)
{a(n)=polcoeff(exp(sum(m=1,n,sumdiv(m,d,d!)*x^m/m)+x*O(x^n)),n)}
Sum_{d|3} d! = 1! + 3! = 7 is prime, so 3 is a member.
seq(`if`(isprime(ithprime(n)!+1), ithprime(n), NULL),n=1..25); # Nathaniel Johnston, Jun 28 2011
Select[Prime[Range[5! ]],PrimeQ[ #!+1]&] (* Vladimir Joseph Stephan Orlovsky, Nov 17 2009 *)
isok(n) = ispseudoprime(n) && ispseudoprime(n!+1); \\ Jinyuan Wang, Jan 20 2020
5 is prime and 5$ + 1 = 30 + 1 = 31 is prime, so 5 is in the sequence.
a := proc(n) select(isprime,select(k -> isprime(A056040(k)+1),[$0..n])) end:
f[n_] := 2^(n - Mod[n, 2])*Product[k^((-1)^(k + 1)), {k, n}]; p = 2; lst = {}; While[p < 38000, a = f@p + 1; If[ PrimeQ@a, AppendTo[ lst, p]; Print@p]; p = NextPrime@p]; lst (* Robert G. Wilson v, Aug 08 2010 *)
is(k) = isprime(k) && ispseudoprime(1+k!/(k\2)!^2); \\ Jinyuan Wang, Mar 22 2020
f[n_]=With[{d=Divisors[n]},Total[(d!)^(n/d)]]; Array[f,25] (* Harvey P. Dale, Dec 20 2023 *)
a(n)=sumdiv(n,d, (d!)^(n/d) );
Table[Sum[(i!)^(n - i) (1 - Ceiling[n/i] + Floor[n/i]), {i, n}], {n, 20}]
a(n) = sumdiv(n, d, d!^(n-d)); \\ Seiichi Manyama, Oct 03 2021
my(N=20, x='x+O('x^N)); Vec(sum(k=1, N, x^k/(1-(k!*x)^k))) \\ Seiichi Manyama, Oct 03 2021
a(6) = 8; a(6) = Sum_{p|6} (6/p)! = (6/2)! + (6/3)! = 3*2 + 2*1 = 8.
f:= proc(n) local p; add((n/p)!, p = numtheory:-factorset(n)) end proc: map(f, [$1..40]); # Robert Israel, Dec 05 2022
Table[DivisorSum[n, Factorial[n/#] &, PrimeQ], {n, 36}] (* Michael De Vlieger, Dec 06 2022 *)
Table[Sum[(-1)^(n/d + 1) d!, {d, Divisors[n]}], {n, 22}] nmax = 22; Rest[CoefficientList[Series[Sum[k! x^k/(1 + x^k), {k, 1, nmax}], {x, 0, nmax}], x]]
a(n) = sumdiv(n, d, (-1)^(n/d+1)*d!); \\ Michel Marcus, Nov 12 2018
m:=25; R:=PowerSeriesRing(Integers(), m); Coefficients(R!( (&+[k*Factorial(k)*x^k/(1 - x^k): k in [1..(m+2)]]) )); // G. C. Greubel, Nov 20 2018
Table[Sum[d d!, {d, Divisors[n]}], {n, 21}] nmax = 21; Rest[CoefficientList[Series[Sum[k k! x^k/(1 - x^k), {k, 1, nmax}], {x, 0, nmax}], x]] nmax = 21; Rest[CoefficientList[Series[-Log[Product[(1 - x^k)^k!, {k, 1, nmax}]], {x, 0, nmax}], x] Range[0, nmax]]
a(n) = sumdiv(n, d, d*d!); \\ Michel Marcus, Nov 20 2018
s = sum(k*factorial(k)*x^k/(1-x^k) for k in (1..24)); (s/x).series(x, 21).coefficients(x, sparse=false) # Peter Luschny, Nov 21 2018
a(6) = 8; a(6) = Sum_{p|6} p! = 2! + 3! = 2*1 + 3*2*1 = 8.
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