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A269903 Integers n such that A002110(n) / 2 is the sum of 4 but no fewer nonzero squares. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified February 19 13:25 EST 2020. Contains 332044 sequences. (Running on oeis4.)