A353033 Numbers m such that tau(m) = 2 * tau(m - 1) and simultaneously sigma(m) = 2 * sigma(m - 1), where tau(k) = A000005(k) and sigma(k) = A000203(k).

6, 47796, 111684, 123498, 224562, 228378, 384858, 773016, 1096824, 1174542, 2351240, 2529414, 3320472, 3332616, 3650376, 4605096, 4838838, 4978476, 5014842, 5788662, 6023928, 6302724, 7658024, 8298978, 9287240, 9967974, 10950024, 12677496, 14036694, 14120360, 14927990

Offset

1,1

Comments

Corresponding values of tau(m): 4, 24, 24, 16, 16, 16, 16, 32, 32, 16, 32, 32, 32, ...

Corresponding values of sigma(m): 12, 127680, 268128, 274560, 483840, 483840, 855360, 1996800, 2862720, 2472960, ...

Links

Table of n, a(n) for n=1..31.

Example

tau(6) = 4 = 2 * tau(5) = 2 * 2, sigma(6) = 12 = 2 * sigma(5) = 2 * 6.

Prog

(Magma) [m: m in [2..10^6] | #Divisors(m) eq 2 * #Divisors(m - 1) and &+Divisors(m) eq 2 * &+Divisors(m - 1)]

Crossrefs

Cf. A000005 (tau), A000203 (sigma), A054004, A347603, A353034.

Sequence in context: A295789 A261626 A013838 * A289391 A295817 A118859

Adjacent sequences: A353030 A353031 A353032 * A353034 A353035 A353036

Keyword

nonn

Author

Jaroslav Krizek, Apr 18 2022

Status

approved