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A078765
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Prime numbers occurring at integer Pythagorean distance (radius) from 1 in Ulam square prime-spiral. Primes on axes are excluded.
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0
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227, 239, 271, 997, 1021, 1061, 2243, 2251, 2311, 2339, 2347, 3527, 4153, 4217, 6311, 6491, 6551, 6971, 9059, 9109, 9133, 9341, 9397, 12671, 14549, 16273, 16369, 16529, 19507, 20551, 20611, 20719, 20899, 20983, 25301, 25343, 25621, 25741, 27893
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Note that prime numbers on an axis are automatically an integer distance from 1.
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EXAMPLE
| a(1) = 227, a prime number: distance from 1 off-axis = (6,8,10) triangle.
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PROG
| (PARI) { uc(n) = k = (sqrtint(4*n-3)-1)\2; d=n-1-k*(k+1); if(k%2, c=[(k+1)\2-min(d, k+1), (k+1)\2-max(d-k-1, 0)], c=[-k\2+min(d, k+1), -k\2+max(d-k-1, 0)] ); c }
forprime(p=2, 10^5, t=uc(p); if( t[1]!=0 && t[2]!=0 && issquare(t[1]^2+t[2]^2), print1(p, ", "))) \\ From Max Alekseyev
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CROSSREFS
| Sequence in context: A098247 A092994 A031513 * A179141 A169610 A142261
Adjacent sequences: A078762 A078763 A078764 * A078766 A078767 A078768
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KEYWORD
| nonn
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AUTHOR
| Donald S. McDonald (don.mcdonald(AT)paradise.net.nz), Jan 09 2003
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EXTENSIONS
| More terms from Max Alekseyev (maxale(AT)gmail.com), Jan 28 2012
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