A337988 Numbers that are the sum of the squares of two of their distinct divisors.

20, 80, 90, 180, 272, 320, 360, 468, 500, 650, 720, 810, 980, 1088, 1280, 1332, 1440, 1620, 1872, 2000, 2250, 2420, 2448, 2450, 2600, 2880, 2900, 3240, 3380, 3600, 3920, 4160, 4212, 4352, 4410, 4500, 5120, 5328, 5760, 5780, 5850, 6480, 6642, 6800, 7220, 7290, 7488, 7650

Offset

1,1

Links

Chai Wah Wu, Table of n, a(n) for n = 1..10000

Index entries for sequences related to sums of squares

Example

20 = 2^2 + 4^2, so 20 is in the sequence.

Mathematica

Select[Range[10^4], 1 == Catch@ Do[Do[If[#2[[i]]^2 + #2[[j]]^2 == #1, Throw[1]], {j, i + 1, #3}], {i, #3}] & @@ {#, Divisors[#], DivisorSigma[0, #]} &] (* Michael De Vlieger, Oct 10 2020 *)

Prog

(PARI) isok(m) = {my(d=divisors(m)); for (i=2, #d, for (j=1, i-1, if (d[i]^2+d[j]^2 == m, return (1)); ); ); } \\ Michel Marcus, Oct 07 2020
(Python)
from sympy import divisors, integer_nthroot
A337988_list = []
for n in range(1, 10**6):
    for d in divisors(n):
        if 2*d*d >= n:
            break
        a, b = integer_nthroot(n-d*d, 2)
        if b and n % a == 0:
            A337988_list.append(n)
            break # Chai Wah Wu, Oct 30 2020

Crossrefs

Cf. A000404.

Sequence in context: A083127 A211613 A292360 * A002609 A195322 A200424

Adjacent sequences: A337985 A337986 A337987 * A337989 A337990 A337991

Keyword

nonn

Author

Wesley Ivan Hurt, Oct 06 2020

Extensions

More terms from Michel Marcus, Oct 07 2020

Status

approved