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A078765 Prime numbers occurring at integer Pythagorean distance (radius) from 1 in Ulam square prime-spiral. Primes on axes are excluded. 0
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; text; internal format)
OFFSET

1,1

COMMENTS

Note that prime numbers on an axis are automatically an integer distance from 1.

LINKS

Table of n, a(n) for n=1..39.

EXAMPLE

a(1) = 227, a prime number: distance from 1 off-axis = (6,8,10) triangle.

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, ", "))) \\ Max Alekseyev

CROSSREFS

Sequence in context: A098247 A092994 A031513 * A179141 A259059 A142261

Adjacent sequences:  A078762 A078763 A078764 * A078766 A078767 A078768

KEYWORD

nonn

AUTHOR

Donald S. McDonald, Jan 09 2003

EXTENSIONS

More terms from Max Alekseyev, Jan 28 2012

STATUS

approved

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Last modified November 18 22:50 EST 2019. Contains 329305 sequences. (Running on oeis4.)