OFFSET
1,1
COMMENTS
FORMULA
a(n) = prime(ceiling(n/2))*(prime(ceiling(n/2)) - (n mod 2))
EXAMPLE
930 is in the sequence because ceiling(sqrt(930)) = 31 and 930/31 = 30.
MATHEMATICA
Flatten[ #(#-{1, 0})&/@Prime/@Range[30]]
a[n_] := (p=Prime[Ceiling[n/2]])(p-Mod[n, 2])
PROG
(PARI) ipsqrt(n) = { sr= 0; for(x=1, n, v = ceil(sqrt(x)); if(isprime(v) && x%v == 0, print1(x" "); sr+=1.0/x; ); ); print(); print(sr); } \\ numbers divisible by the prime ceilings of their square roots.
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Cino Hilliard, Dec 26 2002
STATUS
approved