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.

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

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

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

Adjacent sequences: A317389 A317390 A317391 * A317393 A317394 A317395

Keyword

nonn

Author

Alois P. Heinz, Jul 27 2018

Status

approved