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A158845
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Prepending 1 to n-th triangular number produces a prime.
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2
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2, 13, 17, 18, 21, 38, 41, 62, 66, 77, 97, 98, 106, 117, 118, 133, 146, 153, 157, 161, 178, 181, 197, 198, 202, 206, 217, 222, 226, 233, 237, 242, 257, 261, 266, 286, 297, 301, 302, 318, 321, 322, 338, 346, 362, 373, 377, 393, 402, 413, 421, 422, 453, 461, 462
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Or, concatenated T(1) and T(n) produces a prime, or, concatenated A000217(1) and A000217(n) produces a prime.
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EXAMPLE
| n=2: T(2)=3, 13 is prime,
n=13: T(13)=91, 191 is prime,
n=17: T(17)=153, 1153 is prime.
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MATHEMATICA
| Rest[Select[Range[600], PrimeQ[FromDigits[Join[{1}, IntegerDigits[(# (#+1))/2]]]]&]] [From Harvey P. Dale (hpd1(AT)nyu.edu), Apr 15 2009]
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CROSSREFS
| A158844 Concatenated triangular numbers T (n), T(n + 1) and T(n + 2) are prime. A158750 Concatenated triangular numbers that are prime. A000217 Triangular numbers.
Sequence in context: A041645 A032453 A065245 * A163786 A153507 A124277
Adjacent sequences: A158842 A158843 A158844 * A158846 A158847 A158848
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KEYWORD
| nonn,base
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AUTHOR
| Zak Seidov (zakseidov(AT)yahoo.com), Mar 28 2009
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