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A111483
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Triangular numbers all of whose digits are primes.
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0
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3, 55, 253, 325, 2775, 5253, 255255, 522753, 577275, 2235555, 2355535, 2532375, 3252525, 3352755, 7332535, 23273253, 25222753, 37372335, 55277355, 73235253, 222552253, 273253753, 325775575, 337337325, 577235253, 2373777253
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OFFSET
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1,1
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COMMENTS
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3 = T(2) and 253 = T(22) have all prime digits and all prime digits in their indices as triangular numbers. What is the next of this subsequence?
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LINKS
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EXAMPLE
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3 = T(2), 55 = T(10), 253 = T(22), 325 = T(25), 2775 = T(74), 5253 = T(102), 255255 = T(714), 522753 = T(1022), 577275 = T(1074), 2235555 = T(2114), 2355535 = T(2170), 2532375 = T(2250).
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MATHEMATICA
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fQ[n_] := Union@Join[{2, 3, 5, 7}, IntegerDigits[n(n + 1)/2]] == {2, 3, 5, 7}; s = Select[ Range[10^5], fQ[ # ] &]; s (s + 1)/2 (* Robert G. Wilson v *)
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CROSSREFS
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KEYWORD
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base,easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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