login
A317392
Positive integers that have exactly two representations of the form 1 + p1 * (1 + p2* ... * (1 + p_j)...), where [p1, ..., p_j] is a (possibly empty) list of distinct primes.
2
25, 29, 37, 40, 41, 49, 51, 52, 67, 71, 77, 85, 87, 88, 89, 97, 103, 112, 115, 123, 125, 126, 127, 130, 137, 139, 145, 146, 148, 149, 155, 157, 161, 169, 175, 181, 183, 186, 191, 199, 202, 209, 214, 217, 222, 223, 229, 232, 235, 238, 239, 241, 243, 248, 249
OFFSET
1,1
LINKS
FORMULA
A317241(a(n)) = 2.
MAPLE
b:= proc(n, s) option remember; local p, r; if n=1 then 1 else r:=0;
for p in numtheory[factorset](n-1) minus s while r<3
do r:= r+b((n-1)/p, s union {p}) od; `if`(r<3, r, 3)
fi
end:
a:= proc(n) option remember; local k; for k from
`if`(n=1, 1, 1+a(n-1)) while b(k, {})<>2 do od; k
end:
seq(a(n), n=1..100);
CROSSREFS
Column k=2 of A317390.
Cf. A317241.
Sequence in context: A334534 A259028 A358425 * A373505 A234640 A219258
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jul 27 2018
STATUS
approved