A206097 Fibonacci numbers F that are squarefree semiprimes such that F+2 or F-2 is also a squarefree semiprime.

55, 4181, 17711, 121393, 5702887

Offset

1,1

Comments

a(6) > Fibonacci(1500), if it exists. - Amiram Eldar, Aug 01 2024

Links

Table of n, a(n) for n=1..5.

Example

55 = Fibonacci(10) is a term because 55 = 5 * 11 and 55 + 2 = 57 = 3 * 19 are both squarefree semiprimes.
4181 = Fibonacci(19) is a term because 4181 = 37 * 113 and 4181 + 2 = 4183 = 47 * 89 are both squarefree semiprimes.

Mathematica

Select[Fibonacci[Range[300]], Last/@FactorInteger[#]=={1, 1} && (Last/@FactorInteger[#+2]=={1, 1} || Last/@FactorInteger[#-2]=={1, 1})&]

Crossrefs

Subsequence of A000045, A006881 and A053409.

Cf. A072381.

Sequence in context: A060077 A035323 A250833 * A103918 A013537 A056567

Adjacent sequences: A206094 A206095 A206096 * A206098 A206099 A206100

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Feb 03 2012

Extensions

Name corrected by Amiram Eldar, Aug 01 2024

Status

approved