OFFSET
1,2
COMMENTS
p divides a(p-1) for prime p>2. p divides a(2p-1) for all prime p. p divides a(3p-1) for all prime p. p divides a(4p-1) for all prime p except p=3. p divides a(5p-1) for prime p>3. p divides a(6p-1) for all prime except p=5. . p^2 divides a(p^2-1) for prime p>2. p^2 divides a(2p^2-1) for all prime p. p^2 divides a(3p^2-1) for all prime p. . p^3 divides a(p^3-1) for prime p>2. . p^k divides a(p^k-1) for prime p>2 and integer k>1. p^k divides a(m*p^k-1) for all prime p and integer m,k>1.
FORMULA
MATHEMATICA
Numerator[Table[Sum[k^2/(n-k+1), {k, 1, n}], {n, 1, 50}]]
CROSSREFS
KEYWORD
frac,nonn
AUTHOR
Alexander Adamchuk, Jul 26 2006
STATUS
approved