cp's OEIS Frontend

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.

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A227644 Perfect powers equal to the sum of 2 factorial numbers.

Original entry on oeis.org

4, 8, 25, 121, 144, 5041
Offset: 1

Views

Author

Giovanni Resta, Jul 19 2013

Keywords

Comments

a(7), if it exists, is greater than 10^100.
a(7), if it exists, is greater than 10000!. - Filip Zaludek, Jul 18 2017
a(7), if it exists, is greater than 11750!. - Filip Zaludek, Sep 07 2018
a(7), if it exists, is greater than 20000!. - Filip Zaludek, Nov 04 2020

Examples

			5041 = 71^2 = 1! + 7!.
		

Crossrefs

Programs

  • C
    /* 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;
    }
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