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A317393
Positive integers that have exactly three representations of the form 1 + p1 * (1 + p2* ... * (1 + p_j)...), where [p1, ..., p_j] is a (possibly empty) list of distinct primes.
2
43, 61, 91, 111, 121, 124, 171, 184, 187, 205, 221, 231, 256, 265, 267, 268, 274, 277, 281, 283, 291, 311, 323, 326, 331, 337, 371, 373, 375, 379, 386, 411, 412, 427, 428, 435, 443, 451, 456, 457, 471, 474, 475, 482, 491, 494, 505, 507, 508, 511, 519, 521, 523
OFFSET
1,1
LINKS
FORMULA
A317241(a(n)) = 3.
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<4
do r:= r+b((n-1)/p, s union {p}) od; `if`(r<4, r, 4)
fi
end:
a:= proc(n) option remember; local k; for k from
`if`(n=1, 1, 1+a(n-1)) while b(k, {})<>3 do od; k
end:
seq(a(n), n=1..100);
CROSSREFS
Column k=3 of A317390.
Cf. A317241.
Sequence in context: A102540 A063641 A129928 * A253848 A245742 A295702
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jul 27 2018
STATUS
approved