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A159935
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Least integer such that a(n)^2 - n is the sum of two nonzero squares.
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1
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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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. */
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CROSSREFS
| Cf. A008846, A050795.
Sequence in context: A052038 A040022 A165100 * A165102 A009661 A023576
Adjacent sequences: A159932 A159933 A159934 * A159936 A159937 A159938
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KEYWORD
| nonn
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AUTHOR
| Franklin T. Adams-Watters (FrankTAW(AT)Netscape.net), Apr 26 2009
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