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 A221310 Numbers m such that exactly four subsets of {m-1, m, m+1} sum up to a prime number. 3
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A117499(a(n)) = 4; (a(n)-1,a(n)+1) are twin prime pairs for n >= 4. LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..1000 EXAMPLE a(1) = 1: the required 4 subsets of {1-1,1,1+1} are: {2}, {0,2}, {1,2} and {0,1,2}. MATHEMATICA Select[Range[170000], Count[Total/@Subsets[{#-1, #, #+1}], _?PrimeQ]==4&] (* Harvey P. Dale, Jul 30 2019 *) PROG (Haskell) a221310 n = a221310_list !! (n-1) a221310_list = map (+ 1) \$ elemIndices 4 a117499_list CROSSREFS 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 KEYWORD nonn AUTHOR Reinhard Zumkeller, Jan 10 2013 STATUS approved

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Last modified April 2 02:53 EDT 2023. Contains 361723 sequences. (Running on oeis4.)