login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A252791 Numbers m such that 6^m + m is a semiprime. 1
2, 3, 5, 7, 11, 23, 41, 55, 73, 91, 131, 199, 221, 287 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..14.

EXAMPLE

2 is in this sequence because 6^2+2 = 2*19 is semiprime.

7 is in this sequence because 6^7+7 = 271*1033 and these two factors are prime.

MATHEMATICA

Select[Range[90], PrimeOmega[6^# + #]==2 &]

PROG

(MAGMA) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..90] | IsSemiprime(s) where s is 6^m+m];

CROSSREFS

Cf. similar sequences listed in A252788.

Cf. A252659.

Sequence in context: A288371 A158217 A030284 * A068148 A036344 A165802

Adjacent sequences:  A252788 A252789 A252790 * A252792 A252793 A252794

KEYWORD

nonn,more

AUTHOR

Vincenzo Librandi, Dec 25 2014

EXTENSIONS

a(10)-a(14) by Luke March, Jul 08 2015

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 26 16:43 EDT 2020. Contains 337374 sequences. (Running on oeis4.)