OFFSET
0,1
COMMENTS
FORMULA
((i + 1)*(i + 2*n))/2 = p, p prime number.
EXAMPLE
n = 4: no such i exists, thus a(4) = -1.
n = 5: n is prime, i = 0, thus a(5) = 0.
n = 6: n + (n + 1) = 6 + 7 = 13 is prime, i = 1, thus a(6) = 1.
CROSSREFS
KEYWORD
sign
AUTHOR
Ctibor O. Zizka, Jun 17 2023
STATUS
approved