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A252792 Numbers m such that 7^m + m is a semiprime. 1
2, 3, 6, 12, 15, 16, 30, 54, 244, 850, 1488 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
2 is in this sequence because 7^2+2 = 3*17 is semiprime.
6 is in this sequence because 7^6+6 = 5*23531 and these two factors are prime.
MATHEMATICA
Select[Range[600], PrimeOmega[7^# + #]==2 &]
PROG
(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..600] | IsSemiprime(s) where s is 7^m+m];
CROSSREFS
Cf. similar sequences listed in A252788.
Cf. A252660.
Sequence in context: A329401 A291174 A281110 * A284638 A111271 A217647
KEYWORD
nonn
AUTHOR
Vincenzo Librandi, Dec 25 2014
EXTENSIONS
a(9) from Carl Schildkraut, Aug 14 2015
a(10) from Kevin P. Thompson, Apr 25 2022
a(11) from Charles R Greathouse IV, Apr 25 2022
STATUS
approved

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Last modified March 28 09:04 EDT 2024. Contains 371240 sequences. (Running on oeis4.)