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A129545
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Triangular numbers T such that T+1 is a prime.
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6
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1, 6, 10, 28, 36, 66, 78, 136, 190, 210, 276, 378, 630, 820, 946, 990, 1128, 1326, 1596, 1830, 2016, 2080, 2346, 2556, 2850, 2926, 3570, 3916, 4560, 4656, 4950, 5050, 5778, 6216, 6328, 8646, 8778, 9180, 9870, 11026, 12720, 13366, 14028, 14196, 14878
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OFFSET
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1,2
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COMMENTS
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The only triangular numbers T such that T-1 is a (positive) prime are 3 and 6.
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LINKS
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FORMULA
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MATHEMATICA
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Select[Accumulate[Range[200]], PrimeQ[#+1]&] (* Harvey P. Dale, Nov 08 2011 *)
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PROG
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(Python)
from sympy import isprime
def T(n): return n*(n+1)//2
def ok(T): return isprime(T+1)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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