OFFSET
0,2
COMMENTS
LINKS
Robert G. Wilson v, Table of n, a(n) for n = 0..1740 (first 216 terms from Robert Israel)
David A. Corneth, Conjectured first 10001 terms.
EXAMPLE
a(3) = 18 has 3 such divisors: 2+1=3, 5+1=6, 17+1=18, and is the least number with exactly 3.
MAPLE
f:= proc(n) nops(select(t -> isprime(t-1), numtheory:-divisors(n))) end proc:
N:= 60: count:= 0:
V:= Array(0..N):
for n from 1 while count < N+1 do
v:= f(n);
if v <= N and V[v] = 0 then
count:=count+1;
V[v]:= n;
fi;
od:
convert(V, list);
MATHEMATICA
With[{s = Array[DivisorSum[#, 1 &, PrimeQ[# - 1] &] &, 10^5]}, Array[FirstPosition[s, #][[1]] &, 51, 0]] (* Michael De Vlieger, Feb 05 2021 *)
PROG
(PARI) a(n) = my(k=1); while (sumdiv(k, d, isprime(d-1)) != n, k++); k; \\ Michel Marcus, Feb 05 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Feb 05 2021
STATUS
approved