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A180161 Numbers that are the sum of two nonnegative squares but are not perfect powers. 0
2, 5, 10, 13, 17, 18, 20, 26, 29, 34, 37, 40, 41, 45, 50, 52, 53, 58, 61, 65, 68, 72, 73, 74, 80, 82, 85, 89, 90, 97, 98, 101, 104, 106, 109, 113, 116, 117, 122, 130, 136, 137, 145, 146, 148, 149, 153, 157, 160, 162, 164, 170, 173, 178, 180, 181, 185, 193, 194, 197, 200, 202, 205, 208, 212, 218, 221, 226, 229, 232, 233 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Terms in A001481 but not in A001597.

LINKS

Table of n, a(n) for n=1..71.

FORMULA

  Numbers of the form 2^i * S^j * T^(2*k) where S is a product of primes 4k+1, T a product of primes 4k+3, i,j,k>=0, and the gcd of the numbers {i, j, 2*k} is 1.

PROG

(PARI)

isA001481(n) =

{

    local(x=0, r=0);

    while(x<=sqrt(n)&r==0, if(issquare(n-x^2), r=1); x++);

    return(r);

}

for(n=2, 1000, if( isA001481(n) && !ispower(n), print1(n, ", ") ) );

CROSSREFS

A001481 (sums of 2 nonnegative squares), A001597 (perfect powers).

Sequence in context: A046462 A188025 A187949 * A099261 A103215 A037942

Adjacent sequences:  A180158 A180159 A180160 * A180162 A180163 A180164

KEYWORD

nonn

AUTHOR

Joerg Arndt, Jan 16 2011

STATUS

approved

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Last modified September 21 15:29 EDT 2017. Contains 292307 sequences.