A173684 Semiprimes of the form Fibonacci(k) + k.

10, 14, 65, 391, 1003, 2602, 10967, 2178341, 701408777, 86267571326, 591286729937, 4052739537943, 72723460248209, 117669030461063, 3416454622906783, 61305790721611673, 420196140727489759, 2427893228399975082557, 251728825683549488150424389

Offset

1,1

Comments

This is to A069108 as semiprimes are to primes. A002062(k) is semiprime for k = 5, 6, 10, 14, 16, 18, 21, 32, ...

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..24

Formula

A002062 INTERSECTION A001358.

Example

F(21) + 21 = 10967 = 11 * 997, thus 10967 is in the sequence.

Mathematica

Select[Table[Fibonacci[n]+n, {n, 200}], PrimeOmega[#]==2&] (* Harvey P. Dale, Nov 02 2011 *)

Prog

(Magma) IsSemiprime:=func< n | &+[ k[2]: k in Factorization(n) ] eq 2 >; [ a: n in [1..100] | IsSemiprime(a) where a is n+Fibonacci(n) ]; // Klaus Brockhaus, Jan 27 2011

Crossrefs

Cf. A000045, A001358, A002062, A053409, A069108.

Sequence in context: A107126 A247091 A025122 * A258287 A254003 A219682

Adjacent sequences: A173681 A173682 A173683 * A173685 A173686 A173687

Keyword

nonn

Author

Jonathan Vos Post, Jan 26 2011

Status

approved