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A325072
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Prime numbers congruent to 1 modulo 20 neither representable by x^2 + 20*y^2 nor by x^2 + 100*y^2.
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3
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41, 61, 241, 281, 421, 601, 641, 661, 701, 821, 881, 1181, 1201, 1301, 1321, 1381, 1481, 1801, 1901, 2141, 2161, 2221, 2281, 2341, 2381, 2521, 2741, 3041, 3061, 3181, 3221, 3361, 3541, 3701, 3761, 4241, 4261, 4421, 4481, 4721, 4801, 5381, 5501, 5521, 5581
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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COMMENTS
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Brink showed that prime numbers congruent to 1 modulo 20 are representable by both or neither of the quadratic forms x^2 + 20*y^2 and x^2 + 100*y^2. A325071 corresponds to those representable by both, and this sequence corresponds to those representable by neither.
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LINKS
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EXAMPLE
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Regarding 2221:
- 2221 is a prime number,
- 2221 = 111*20 + 1,
- 2221 is neither representable by x^2 + 20*y^2 nor by x^2 + 100*y^2,
- hence 2221 belongs to this sequence.
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PROG
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(PARI) See Links section.
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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