A361797 Even numbers k which have fewer divisors than both neighboring odd numbers, i.e., tau(k) < min{tau(k-1), tau(k+1)}.

274, 386, 626, 926, 1126, 1174, 1234, 1546, 1574, 1594, 1646, 1774, 1814, 1954, 2036, 2066, 2092, 2186, 2234, 2276, 2302, 2374, 2386, 2402, 2404, 2554, 2638, 2738, 2876, 2906, 3158, 3244, 3334, 3394, 3446, 3554, 3566, 3574, 3758, 3814, 3994, 4124, 4166, 4174

Offset: 1

Author

Steven Lu, Mar 25 2023

Keywords

• nonn

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Even terms of A075025. Cf. A000005.

Programs

Maple

Tau:= map(numtheory:-tau, [$1..10001]):
select(t -> Tau[t] < Tau[t-1] and Tau[t] < Tau[t+1], [seq(i,i=2..10000,2)]); # Robert Israel, Mar 28 2023

Mathematica

Select[2 Range[10000],
 DivisorSigma[0, #] < DivisorSigma[0, # + 1] &&
   DivisorSigma[0, #] < DivisorSigma[0, # - 1] &]

PARI

isok(k) = !(k%2) && (numdiv(k) < min(numdiv(k-1), numdiv(k+1))); \\ Michel Marcus, Mar 26 2023