A159935 Least integer such that a(n)^2 - n is the sum of two nonzero squares.

5, 3, 2, 4, 3, 5, 4, 3, 4, 7, 6, 4, 5, 9, 4, 5, 6, 5, 6, 6, 5, 11, 12, 5, 7, 15, 6, 8, 6, 7, 8, 6, 7, 13, 6, 8, 7, 21, 8, 7, 9, 7, 10, 12, 7, 15, 8, 7, 10, 9, 10, 8, 9, 11, 8, 9, 8, 17, 30, 8, 10, 9, 8, 9, 9, 13, 10, 18, 9, 11, 12, 9, 12, 9, 10, 10, 9, 15, 16, 9, 10, 11, 10, 10, 11, 21, 12, 10, 15

Offset

0,1

Links

Table of n, a(n) for n=0..88.

Prog

(PARI) issum2sq(n) = local(fm, hf); hf=0; fm=factor(n); for(i=1, matsize(fm)[1], if(fm[i, 1]==2, if(fm[i, 2]%2, hf=1), if(fm[i, 1]%4==1, hf=1, if(fm[i, 2]%2, return(0))))); hf
minsum2sq(n) = local(k); k=1; while(!issum2sq(k^2-n), k++); k
/* Note: the issum2sq function depends on PARI returning -1 as a factor for negative n. */

Crossrefs

Cf. A008846, A050795.

Sequence in context: A040022 A165100 A351061 * A165102 A294568 A290349

Adjacent sequences: A159932 A159933 A159934 * A159936 A159937 A159938

Keyword

nonn

Author

Franklin T. Adams-Watters, Apr 26 2009

Status

approved