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A066828
Numbers k that divide the average of prime(k-1) and prime(k+1).
0
4, 5, 11, 12, 70, 72, 1053, 6459, 6460, 40083, 251742, 637320, 637322, 637330, 10553828, 69709721, 179992913, 179992922, 465769813, 1208198617, 1208198629, 3140421742, 3140421769, 3140421866, 8179002192, 8179002205, 8179002209
OFFSET
1,1
COMMENTS
Each cluster of candidates is about e (2.71828...) times as large as the previous one.
EXAMPLE
The average of prime(4) = 7 and prime(6) = 13 is 10, which is divisible by 5, so 5 is a term of the sequence.
MATHEMATICA
a = 0; b = 1; c = 2; Do[ c = Prime[ n + 1 ]; If[ IntegerQ[ (a + c)/(2n) ], Print[ n ] ]; a = b; b = c, {n, 1, 2 10^9} ]
CROSSREFS
Cf. A066706.
Sequence in context: A047374 A241653 A100107 * A163098 A216562 A174009
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Jan 20 2002
STATUS
approved