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Search: id:A106215
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| A106215 |
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The first n primes, connected by, from left to right, alternating + and * signs. |
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+0
1
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| 2, 5, 17, 24, 94, 107, 315, 334, 752, 781, 1651, 1688, 3168, 3211, 5189, 5242, 8316, 8377, 12403, 12474, 17586, 17665, 24143, 24232, 32776, 32877, 43179, 43286, 54842, 54955, 69193, 69324, 87140, 87279, 107851, 108002, 131558, 131721, 158779
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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a(n) is prime for n = 1, 2, 3, 6, 15, 18, 31, 43, 82, ... a(n) is semiprime for n = 5, 8, 10, 11, 16, 19, 22, 23, 35, 36, 39, 41, 47, 50, 55, 56, 58, 63, 65, 66, 80, 83, ...
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EXAMPLE
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a(1) = 2, itself a prime;
a(2) = 2+3 = 5, itself a prime;
a(3) = 2+3*5 = 17, itself a prime;
a(4) = 2+3*5+7 = 24;
a(5) = 2+3*5+7*11 = 94;
a(15) = 2+3*5+7*11+13*17+19*23+29*31+37*41+43*47 = 5189, prime;
a(31) =
2+3*5+7*11+13*17+19*23+29*31+37*41+43*47+53*59+61*67+71*73+79*83+89*97+101*103+107*109+113*127 = 69193, which is prime.
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CROSSREFS
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Sequence in context: A023244 A023867 A024594 this_sequence A077217 A120847 A019353
Adjacent sequences: A106212 A106213 A106214 this_sequence A106216 A106217 A106218
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost2(AT)yahoo.com), Jul 12 2005
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