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A221310
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Numbers m such that exactly four subsets of {m-1, m, m+1} sum up to a prime number.
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3
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1, 2, 3, 6, 30, 660, 810, 2130, 2550, 3330, 3390, 5850, 6270, 10530, 33180, 41610, 44130, 53550, 55440, 57330, 63840, 65100, 70380, 70980, 72270, 74100, 74760, 78780, 80670, 81930, 87540, 93240, 102300, 115470, 124770, 133980, 136950, 156420, 161460, 168450
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OFFSET
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1,2
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COMMENTS
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A117499(a(n)) = 4;
(a(n)-1,a(n)+1) are twin prime pairs for n >= 4.
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LINKS
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Reinhard Zumkeller, Table of n, a(n) for n = 1..1000
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EXAMPLE
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a(1) = 1: the required 4 subsets of {1-1,1,1+1} are: {2}, {0,2}, {1,2} and {0,1,2}.
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MATHEMATICA
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Select[Range[170000], Count[Total/@Subsets[{#-1, #, #+1}], _?PrimeQ]==4&] (* Harvey P. Dale, Jul 30 2019 *)
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PROG
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(Haskell)
a221310 n = a221310_list !! (n-1)
a221310_list = map (+ 1) $ elemIndices 4 a117499_list
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CROSSREFS
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Subsequence of A040040, apart from a(1)=1.
Sequence in context: A002234 A074005 A145499 * A082611 A033689 A018324
Adjacent sequences: A221307 A221308 A221309 * A221311 A221312 A221313
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KEYWORD
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nonn
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AUTHOR
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Reinhard Zumkeller, Jan 10 2013
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STATUS
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approved
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