OFFSET
1,1
COMMENTS
A lower bound for the 2-color van der Waerden number A005346(prime(n)); see Berlekamp reference. - Charles R Greathouse IV, Jul 13 2008
LINKS
E. R. Berlekamp, A construction for partitions which avoid long arithmetic progressions, Canadian Mathematical Bulletin, Vol. 11, No. 3 (1968), pp. 409-414.
FORMULA
Sum_{n>=1} 1/a(n) = A157413. - Amiram Eldar, Nov 17 2020
MAPLE
seq(ithprime(n)*2^ithprime(n), n=1..20);
MATHEMATICA
#*2^#&/@Prime[Range[20]] (* Harvey P. Dale, Sep 18 2020 *)
PROG
(PARI) a(n) = prime(n)*2^prime(n); \\ Michel Marcus, May 14 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Jorge Coveiro, Dec 26 2004
STATUS
approved