OFFSET
1,1
COMMENTS
The motivation is that n*(n+3)/2 = n + T(n), where T(n) = n*(n+1)/2 = A000217(n), the triangular numbers.
FORMULA
EXAMPLE
For n = 5, n + T(n) = 5 + 15 = 20. The smallest prime factor of 20 is 2, so a(5) = 2.
MATHEMATICA
Array[FactorInteger[# (# + 3)/2][[1, 1]] &, 77] (* Amiram Eldar, Nov 02 2019 *)
PROG
CROSSREFS
KEYWORD
nonn
AUTHOR
Ali Sada, Oct 28 2019
EXTENSIONS
Simpler definition from M. F. Hasler, Nov 10 2019
STATUS
approved