OFFSET
1,1
COMMENTS
Also composite squarefree numbers n such that (2*p(i)+1) | (2*n+1).
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..65 (terms < 3*10^12)
EXAMPLE
The prime factors of 13702 are 2, 13, 17 and 31. We see that (13702 + 1)/(2 + 1/2) = 5481, (13702 + 1/2)/(13 + 1/2) = 1015, (13702 + 1)/(17 + 1/2) = 783 and ( 13702 + 1/2)/(31 + 1/2) = 435. Hence 13702 is in the sequence.
The prime factors of 1123545 are 3, 5 and 74903. We see that
(1123545 + 1/2)/(3 + 1/2) = 321013, (1123545 + 1/2)/(5 + 1/2) = 204281 but (1123545 + 1/2)/(74903+ 1/2) = 321013/21401. Hence 1123545 is not in the sequence.
MAPLE
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
Paolo P. Lava, May 23 2013
EXTENSIONS
a(9)-a(23) from Giovanni Resta, Jun 02 2013
STATUS
approved