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!)
A252793 Numbers m such that 8^m + m is a semiprime. 1
1, 3, 5, 7, 11, 15, 21, 25, 75, 107, 221, 257, 273 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Next terms: 347?, 479, 521, 551, .... - Charles R Greathouse IV, Aug 17 2015

LINKS

Table of n, a(n) for n=1..13.

FORMULA

1 is in this sequence because 8^1+1 = 3*3 is semiprime.

7 is in this sequence because 8^7+7 = 3*699053 and these two factors are prime.

MATHEMATICA

Select[Range[70], PrimeOmega[8^# + #]==2 &]

PROG

(MAGMA) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..70] | IsSemiprime(s) where s is 8^m+m];

(PARI) is(n)=bigomega(8^n+n)==2 \\ Charles R Greathouse IV, Aug 14 2015

CROSSREFS

Cf. similar sequences listed in A252788.

Cf. A252661.

Sequence in context: A337217 A333380 A177139 * A062488 A316936 A116582

Adjacent sequences:  A252790 A252791 A252792 * A252794 A252795 A252796

KEYWORD

nonn

AUTHOR

Vincenzo Librandi, Dec 25 2014

EXTENSIONS

a(9)-a(10) from Luke March, Jul 26 2015

a(11) from Carl Schildkraut, Aug 14 2015

a(12)-a(13) from Charles R Greathouse IV, Aug 17 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.)