OFFSET
1,1
EXAMPLE
If n = 15 = 2*3 (number of prime factors = 2) and n+1 = 16 = 2*2*2*2 (number of prime factors = 4), then 15*16/2 = 120 = a(1). If n = 26 = 2*13 (number of prime factors = 2) and n+1 = 27 = 3**3*3 (number of prime factors = 3), then 26*27/2 = 351 = a(2). If n = 35 = 5*7 (number of prime factors = 2) and n+1 = 36 = 2*2*3*3 (number of prime factors = 4), then 35*36/2 = 630 = a(3), etc.
MATHEMATICA
fQ[n_] := !PrimeQ@ n && Plus @@ Last /@ FactorInteger@n < Plus @@ Last /@ FactorInteger[n + 1]; # (# + 1)/2 & /@ Select[ Range@ 209, fQ@# &] - Robert G. Wilson v, Dec 21 2008
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Dec 15 2008
EXTENSIONS
Edited by Robert G. Wilson v, Dec 21 2008
STATUS
approved