OFFSET
1,1
FORMULA
A000005(a(n) + 1) = 2n.
EXAMPLE
a(4) = 23 because 23 is the smallest prime p such that p + 1 has 2*4 divisors; tau(24) = 8.
PROG
(Magma) Ax:=func<n|exists(r){m:m in[1..10^7] | IsPrime(m) and #Divisors(m + 1) eq n*#Divisors(m)}select r else 0>; [Ax(n): n in[1..20]]
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Jan 21 2021
STATUS
approved