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Search: id:A110891
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| A110891 |
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Numbers of the form prime(n) + prime(n+1) - 2 that are also triangular numbers, T(k) = k(k+1)/2. |
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| 3, 6, 10, 28, 66, 136, 666, 1540, 2278, 3160, 3486, 4186, 5050, 6328, 8128, 9730, 11476, 13366, 15400, 16110, 24090, 24976, 27730, 29646, 32896, 37950, 39340, 46360, 69378, 76636, 81406, 84666, 95266, 98346, 100576, 111628, 123256, 128778
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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a(1) = 3 because prime(1) + prime(2) - 2 = 2 + 3 - 2 = 3 = T(2);
a(2) = 6 because prime(2) + prime(3) - 2 = 3 + 5 - 2 = 6 = T(3);
a(5) = 66 because prime(11) + prime(12) - 2 = 31 + 37 - 2 = 66 = T(11);
a(6) = 136 because prime(19) + prime(20) - 2 = 67 + 71 - 2 = 136 = T(16).
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MATHEMATICA
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Select[Table[Prime[n] + Prime[n + 1] - 2, {n, 7000}], IntegerQ[Sqrt[1 + 8# ]] &] (*Chandler*)
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CROSSREFS
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Cf. A000217 (triangular numbers), A001043 (sum of successive primes).
Sequence in context: A137173 A116544 A068866 this_sequence A115887 A068195 A080506
Adjacent sequences: A110888 A110889 A110890 this_sequence A110892 A110893 A110894
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KEYWORD
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easy,nonn
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AUTHOR
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Giovanni Teofilatto (g.teofilatto(AT)tiscalinet.it), Sep 20 2005
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EXTENSIONS
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Edited and extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Oct 07 2005
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