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
KEYWORD
nonn,easy,less
AUTHOR
Juri-Stepan Gerasimov, Feb 03 2010
EXTENSIONS
Corrected and extended by Emeric Deutsch, Feb 15 2010
Comment from Charles R Greathouse IV, Mar 25 2010
STATUS
approved