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A172462
Numbers k such that 2k-3, 2k-1, 2k+1 and 2k+3 are composite.
0
59, 60, 61, 72, 93, 102, 103, 108, 109, 123, 144, 149, 150, 151, 161, 162, 163, 171, 207, 213, 236, 237, 257, 258, 264, 265, 266, 267, 268, 276, 291, 312, 313, 318, 333, 334, 348, 357, 389, 390, 391, 396, 401, 402, 408, 417, 422, 423, 424, 434, 435, 436, 446
OFFSET
1,1
COMMENTS
Almost all numbers are in this sequence, by the Prime Number Theorem.
EXAMPLE
a(1)=59 because 2*59-1=117, 2*59+1=119, 2*59-3=115 and 2*59+3=121 are all composite.
MAPLE
a := proc (n): if isprime(2*n-3) = false and isprime(2*n-1) = false and isprime(2*n+1) = false and isprime(2*n+3) = false then n else end if end proc: seq(a(n), n = 1 .. 500); # Emeric Deutsch, Feb 15 2010
CROSSREFS
Cf. A104278.
Sequence in context: A273183 A292093 A104916 * A042739 A348570 A172256
KEYWORD
nonn,easy,less
AUTHOR
EXTENSIONS
Corrected and extended by Emeric Deutsch, Feb 15 2010
Comment from Charles R Greathouse IV, Mar 25 2010
STATUS
approved