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Search: id:A105720
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| A105720 |
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Triangular matchstick numbers in the class of prime numbers: sum of n-th and next n primes. |
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| 5, 15, 36, 67, 112, 169, 240, 323, 424, 539, 662, 803, 964, 1133, 1312, 1523, 1746, 1987, 2246, 2519, 2808, 3119, 3436, 3787, 4154, 4529, 4920, 5337, 5770, 6219, 6682, 7173, 7672, 8203, 8760, 9323, 9912, 10517, 11140, 11783, 12450, 13135, 13836
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Cf. A045943 Triangular matchstick numbers: sum of n and next n integers; a(n) are full squares at only(?) three values of n = 3, 6, 4072: {6,13,15735}^2;a(n) are primes at many values of for n = 1,4,16,18,22,36,40,44,52,...: 5,67,1523,1987,3119,9323,11783,14551,21019,...
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FORMULA
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a(n)=p(n)+p(n+1)+...+p(2n-1)+p(2n), p(k)=k-th prime
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MATHEMATICA
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a[n_]:=Plus@@Prime[Range[n, 2n]]
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CROSSREFS
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Cf. A045943.
Sequence in context: A056413 A032276 A065780 this_sequence A011933 A093802 A006008
Adjacent sequences: A105717 A105718 A105719 this_sequence A105721 A105722 A105723
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KEYWORD
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nonn
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AUTHOR
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Zak Seidov (zakseidov(AT)yahoo.com), May 04 2005
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