A269903 Integers n such that A002110(n) / 2 is the sum of 4 but no fewer nonzero squares.

3, 6, 7, 10, 14, 17, 20, 21, 26, 29, 30, 37, 40, 43, 44, 47, 50, 51, 58, 63, 67, 68, 72, 75, 82, 85, 90, 94, 97, 98, 102, 105, 106, 117, 120, 123, 125, 127, 129, 132, 139, 140, 143, 146, 150, 154, 164, 165, 167, 170, 173, 174, 178, 186, 190, 191, 193, 201, 205, 208, 209, 213, 220

Offset

1,1

Links

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

Example

3 is a term because 3*5 = x^2 + y^2 + z^2 where x, y, z are integers is not soluble.
6 is a term because 3*5*7*11*13 = x^2 + y^2 + z^2 where x, y, z are integers is not soluble.
4 is not a term because 3*5*7 = x^2 + y^2 + z^2 where x, y, z are integers is soluble, 105 = 1^2 + 2^2 + 10^2.

Prog

(PARI) isA004215(n) = { my(fouri, j) ; fouri=1 ; while( n >=7*fouri, if( n % fouri ==0, j= n/fouri-7 ; if( j % 8==0, return(1) ) ; ); fouri *= 4 ; ) ; return(0) ; }
for(n=2, 1e3, if(isA004215(prod(k=2, n, prime(k))), print1(n, ", ")));
(Python)
from sympy import prime
A269903_list, p = [], 1
for i in range(2, 10**6):
    p = (p*prime(i)) % 8
    if p == 7:
        A269903_list.append(i) # Chai Wah Wu, Mar 07 2016

Crossrefs

Cf. A002110, A004215.

Sequence in context: A284625 A047281 A182909 * A191103 A100468 A190685

Adjacent sequences: A269900 A269901 A269902 * A269904 A269905 A269906

Keyword

nonn

Author

Altug Alkan, Mar 07 2016

Status

approved