A361797 - OEIS

A361797

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

%I #44 Jan 29 2025 19:29:13

%S 274,386,626,926,1126,1174,1234,1546,1574,1594,1646,1774,1814,1954,

%T 2036,2066,2092,2186,2234,2276,2302,2374,2386,2402,2404,2554,2638,

%U 2738,2876,2906,3158,3244,3334,3394,3446,3554,3566,3574,3758,3814,3994,4124,4166,4174

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

%H Robert Israel, <a href="/A361797/b361797.txt">Table of n, a(n) for n = 1..10000</a>

%p Tau:= map(numtheory:-tau, [$1..10001]):

%p select(t -> Tau[t] < Tau[t-1] and Tau[t] < Tau[t+1], [seq(i,i=2..10000,2)]); # _Robert Israel_, Mar 28 2023

%t Select[2 Range[10000],

%t DivisorSigma[0, #] < DivisorSigma[0, # + 1] &&

%t DivisorSigma[0, #] < DivisorSigma[0, # - 1] &]

%o (PARI) isok(k) = !(k%2) && (numdiv(k) < min(numdiv(k-1), numdiv(k+1))); \\ _Michel Marcus_, Mar 26 2023

%Y Even terms of A075025. Cf. A000005.

%K nonn

%O 1,1

%A _Steven Lu_, Mar 25 2023