OFFSET
1,1
COMMENTS
Consecutive t satisfying the equation a(t) = 2 are consecutive elements of A028982 (squares and twice squares).
EXAMPLE
a(10) = 6 because sigma(10) = 18 is divisible by (tau(1) = 1), (tau(2) = 2), (tau(3) = 2), (tau(4) = 3), (tau(5) = 2), and is not divisible by (tau(6) = 4).
MATHEMATICA
Array[Block[{k = 1}, While[Mod[DivisorSigma[1, #], DivisorSigma[0, k]] == 0, k++]; k] &, 66] (* Michael De Vlieger, Jan 31 2020 *)
PROG
(Maxima) a(n):=(for k:1 while mod(divsum(n), length(divisors(k))) = 0 do z:k, z+1) $ makelist(a(n), n, 1, 100, 1);
(PARI) a(n) = my(k=1, sn=sigma(n)); while ((sn % numdiv(k)) == 0, k++); k; \\ Michel Marcus, Jan 10 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Lechoslaw Ratajczak, Jan 10 2020
STATUS
approved