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A169628
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Semi-sums (average) of two (not necessarily distinct) Mersenne primes (A000668).
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1
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3, 5, 7, 17, 19, 31, 65, 67, 79, 127, 4097, 4099, 4111, 4159, 8191, 65537, 65539, 65551, 65599, 69631, 131071, 262145, 262147, 262159, 262207, 266239, 327679, 524287, 1073741825, 1073741827, 1073741839, 1073741887, 1073745919, 1073807359
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OFFSET
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1,1
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COMMENTS
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Since all terms of A000668 are odd, the semi-sum of any two terms is integer. This motivated introduction of this sequence, A169628 = 1/2 * A171251, see there for further information.
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LINKS
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FORMULA
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EXAMPLE
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MATHEMATICA
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Union[Mean/@Tuples[Select[2^Prime[Range[20]]-1, PrimeQ], {2}]] (* Harvey P. Dale, Mar 12 2011 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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