A395014 - OEIS

%I #18 Apr 15 2026 18:30:24

%S 20,56,66,70,78,88,100,102,104,112,114,138,174,176,186,196,208,220,

%T 222,224,246,258,260,272,282,304,308,318,340,350,352,354,364,366,368,

%U 380,392,402,416,426,438,448,460,464,474,476,490,498,500,532,534,544,550

%N Abundant numbers k for which the k-th Fibonacci number is deficient.

%H Sean A. Irvine, <a href="/A395014/b395014.txt">Table of n, a(n) for n = 1..278</a> (terms 1..137 from Shyam Sunder Gupta)

%e a(1) = 20 is a term because 20 is an abundant number as the sum of the aliquot divisors of 20, i.e., 1 + 2 + 4 + 5 + 10 = 22, is more than 20, and 20th Fibonacci number; i.e., 6765 is a deficient number.

%t A395014Q[k_] := DivisorSigma[1, k] > 2*k && (DivisorSigma[1, #] < 2*# & [Fibonacci[k]]);

%t Select[Range[500], A395014Q] (* _Paolo Xausa_, Apr 15 2026 *)

%o (PARI) isok(k) = if (sigma(k) > 2*k, my(f=fibonacci(k)); sigma(f) < 2*f); \\ _Michel Marcus_, Apr 10 2026

%Y Cf. A000045, A005100, A005101, A074316, A074317, A395013.

%K nonn

%O 1,1

%A _Shyam Sunder Gupta_, Apr 10 2026