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A225861
Numbers n such that (n + prime(n))/2 is a prime.
2
15, 19, 21, 23, 25, 31, 37, 39, 57, 67, 75, 77, 83, 99, 107, 111, 115, 145, 165, 175, 189, 195, 207, 235, 237, 247, 273, 293, 303, 311, 315, 337, 351, 353, 361, 395, 405, 439, 445, 471, 477, 493, 495, 499, 537, 545, 555, 567, 569, 581, 585, 591, 619, 631
OFFSET
1,1
COMMENTS
Average of n and n-th prime is a prime. All n must be odd.
LINKS
EXAMPLE
15 is in the list since (15+Prime(15))/2=31.
MATHEMATICA
Select[Range[632], PrimeQ[(# + Prime[#])/2] &]
CROSSREFS
Cf. A000040.
Sequence in context: A181664 A348517 A224535 * A329184 A077349 A368827
KEYWORD
nonn
AUTHOR
Jayanta Basu, May 18 2013
STATUS
approved