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A332740
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Prime numbers p such that the set of composite numbers in the range [p+1, nextprime(p)-1] has more than one element and all the elements have the same number of divisors.
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1
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229, 8293, 9829, 14887, 16087, 20389, 21493, 44983, 50581, 53887, 57943, 63463, 64663, 72223, 81547, 93253, 108343, 134917, 138727, 143239, 157207, 192613, 199669, 203653, 206407, 210853, 218839, 244837, 248749, 251287, 255049, 262693, 280183, 296437, 300319
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OFFSET
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1,1
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COMMENTS
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The corresponding numbers of divisors are 8, 16, 8, 8, 8, 8, 8, 8, 8, 16, 8, 8, 16, 24, 24, ... and the number of divisors in the order of their first appearance are 8, 16, 24, 20, 12, 32, 48, ...
The number of composites between a(n) and its next prime are 3, 3, 3, 3, 3, 3, 5, 3, 5, 3, ... Are there terms with number of composites larger than 5?
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LINKS
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Amiram Eldar, Table of n, a(n) for n = 1..10000
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EXAMPLE
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229 is a term since between 229 and its next prime, 233, there are 3 composite numbers, 230, 231 and 232 and all of them have the same number of divisors, 8.
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MATHEMATICA
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seqQ[n_] := PrimeQ[n] && (nx=NextPrime[n]) > n + 2 && Length @ Union @ DivisorSigma[0, Range[n+1, nx-1]] == 1; Select[Range[10^6], seqQ]
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CROSSREFS
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Cf. A000005, A075580, A075583, A075584, A075585, A075586, A075587, A075588, A075589.
Sequence in context: A210514 A142665 A124684 * A178673 A028452 A072020
Adjacent sequences: A332737 A332738 A332739 * A332741 A332742 A332743
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KEYWORD
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nonn
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AUTHOR
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Amiram Eldar, Feb 21 2020
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STATUS
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approved
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