A227644
Perfect powers equal to the sum of 2 factorial numbers.
Original entry on oeis.org
4, 8, 25, 121, 144, 5041
Offset: 1
-
/* To compile: gcc -Wall -O2 A227644.c -o A227644 -lgmp */
#include
#include
#include
int main()
{
int bsz=256, a=0;
mpz_t *f, t;
f = malloc(sizeof(mpz_t) * bsz);
mpz_init(t); mpz_init(f[0]); mpz_set_ui(f[0], 1);
while (1)
{
a += 1;
if (a == bsz)
{
bsz *= 2;
f = (mpz_t *) realloc(f, sizeof(mpz_t) * bsz);
}
mpz_init(f[a]);
mpz_mul_ui(f[a], f[a-1], a);
for (int i=1; i<=a; i++)
{
mpz_add(t, f[a], f[i]);
if (mpz_perfect_power_p(t))
{
gmp_printf("%Zd, ", t);
fflush(stdout);
}
}
}
return 0;
}
A162681
Numbers k such that k^2 is a sum of three factorials.
Original entry on oeis.org
2, 3, 6, 7, 29, 72
Offset: 1
2^2 = 1! + 1! + 2!;
3^2 = 1! + 2! + 3!;
6^2 = 3! + 3! + 4!;
7^2 = 1! + 4! + 4!;
29^2 = 1! + 5! + 6!;
72^2 = 4! + 5! + 7!.
-
s := 10^40 ; sqr := s^2 : for a from 1 do if a! > sqr then break; fi; for b from a do if a!+b! > sqr then break; fi; for c from b do if a!+b!+c! > sqr then break; fi; if issqr(a!+b!+c!) then print( sqrt(a!+b!+c!)); fi; od: od: od: # R. J. Mathar, Jul 16 2009
w := 7: f := proc (x, y, z) options operator, arrow: sqrt(factorial(x)+factorial(y)+factorial(z)) end proc: A := {}: for x to w do for y to w do for z to w do if type(f(x, y, z), integer) = true then A := `union`(A, {f(x, y, z)}) else end if end do end do end do: A; # Emeric Deutsch, Aug 03 2009
-
$MaxExtraPrecision=Infinity; lst={};Do[Do[Do[x=(a!+b!+c!)^(1/2);If[x==IntegerPart[x], AppendTo[lst,x]],{c,b,2*4!}],{b,a,2*4!}],{a,2*4!}];Union[lst]
Showing 1-2 of 2 results.
Comments