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A109197
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Minimal value of k>0 such that n^2 + k^2 is semiprime.
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10
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2, 3, 9, 1, 3, 1, 7, 3, 1, 1, 11, 1, 1, 3, 3, 1, 3, 3, 11, 1, 9, 2, 1, 2, 11, 1, 3, 4, 1, 1, 1, 2, 7, 5, 1, 1, 7, 4, 5, 1, 7, 2, 1, 2, 1, 1, 1, 3, 1, 1, 1, 1, 1, 2, 5, 2, 5, 4, 1, 1, 1, 1, 1, 2, 1, 1, 5, 7, 3, 1, 9, 1, 11, 4, 3, 2, 1, 2, 1, 1, 1, 14, 5, 2, 5, 1, 1, 5, 1, 6, 7, 2, 1, 2, 7, 1, 1, 6, 13, 8, 1
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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FORMULA
| a(n) = minimal value of k>0 such that n^2 + k^2 is semiprime.
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EXAMPLE
| a(0) = 2 because 0^2 + 1^2 = 1 is not semiprime, but 0^2 + 2^2 = 4 = 2^2 is.
a(1) = 3 because 1^2 + 1^2 and 1^2 + 2^2 are not semiprime, but 1^2 + 3^2 = 10 = 2 * 5 is semiprime.
a(81) = 14 because 81^2 + 14^2 = 6757 = 29 * 233 and for no smaller k>0 is 81^2 + k^2 a semiprime.
a(100) = 1 because 100^2 + 1^2 = 10001 = 73 * 137.
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PROG
| (PARI) A109197(n)={local(r); r=1; while(bigomega(n^2+r^2)<>2, r=r+1); r} [From Michael B. Porter (michael_b_porter(AT)yahoo.com), May 13 2010]
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CROSSREFS
| Cf. A001358, A108714.
Sequence in context: A011163 A155983 A201407 * A021811 A030367 A028508
Adjacent sequences: A109194 A109195 A109196 * A109198 A109199 A109200
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KEYWORD
| easy,nonn
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AUTHOR
| Jonathan Vos Post (jvospost3(AT)gmail.com), Jun 21 2005
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