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.

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

Alois P. Heinz, Table of n, a(n) for n = 1..20000

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

Adjacent sequences: A317390 A317391 A317392 * A317394 A317395 A317396

Keyword

nonn

Author

Alois P. Heinz, Jul 27 2018

Status

approved