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A125853
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Squared radii of circles centered at a grid point in a square lattice hitting exactly 4 points. Indices k such that A004018(k)=4.
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1
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1, 2, 4, 8, 9, 16, 18, 32, 36, 49, 64, 72, 81, 98, 121, 128, 144, 162, 196, 242, 256, 288, 324, 361, 392, 441, 484, 512, 529, 576, 648, 722, 729, 784, 882, 961, 968, 1024, 1058, 1089, 1152, 1296, 1444, 1458, 1568, 1764, 1849, 1922, 1936, 2048, 2116, 2178, 2209
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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LINKS
| Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 18 2007, Table of n, a(n) for n = 1..501
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FORMULA
| Numbers of the form 2^e0 * 3^(2*e1) * 7^(2*e2) * 11^(2*e3) * ... * qk^(2*ek) where qk is the k-th prime of the form 4*n+3 (A002145). - Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 17 2007
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PROG
| (PARI) for(n=1, 100000, fctrs=factor(n); c=1; for(i=1, matsize(fctrs)[1], p4=fctrs[i, 1]%4; if(p4==1||(p4==3 && fctrs[i, 2]%2==1), c=0)); if(c, print1(n", "))) - Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 17 2007
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CROSSREFS
| Cf. A004018.
Sequence in context: A071601 A114400 A023898 * A080025 A152111 A025611
Adjacent sequences: A125850 A125851 A125852 * A125854 A125855 A125856
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KEYWORD
| nonn
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AUTHOR
| Hugo Pfoertner (hugo(AT)pfoertner.org), Jan 07 2007
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