A395013 - OEIS

A395013

Deficient numbers k for which the k-th Fibonacci number is abundant.

225, 315, 525, 675, 735, 855, 1125, 1155

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OFFSET

1,1

COMMENTS

All terms known so far (up to 1155) are multiples of 15, will this always be true? - M. F. Hasler, Apr 11 2026

From Alexander Violette, Apr 14 2026: (Start)

1485, 1995, and 9975 are terms of this sequence.

If k is a term, then all numbers of the form k*x where k*x is deficient are part of this sequence. (End)

LINKS

Table of n, a(n) for n=1..8.

EXAMPLE

a(1) = 225 is a term because 225 is a deficient number as the sum of the aliquot divisors of 225, i.e., 1 + 3 + 5 + 9 + 15 + 25 + 45 + 75 = 178, is less than 225, and 225th Fibonacci number, i.e., 47068900554068939361891195233676009091941690850 is an abundant number.

PROG

(PARI) is_A395013(n)=sigma(n, -1)<2&&sigma(fibonacci(n), -1)>2 \\ M. F. Hasler, Apr 11 2026

CROSSREFS

Intersection of A005100 and A074726.

Cf. A000045, A005101, A074316, A074317, A395014.

Sequence in context: A044871 A202005 A386640 * A359598 A207639 A077347

Adjacent sequences: A395010 A395011 A395012 * A395014 A395015 A395016

KEYWORD

nonn,hard,more

AUTHOR

Shyam Sunder Gupta, Apr 10 2026

STATUS

approved