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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(10) > 600. - Carl Schildkraut, Aug 14 2015

LINKS

Table of n, a(n) for n=1..9.

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

Adjacent sequences:  A252789 A252790 A252791 * A252793 A252794 A252795

KEYWORD

nonn,more

AUTHOR

Vincenzo Librandi, Dec 25 2014

EXTENSIONS

a(9) from Carl Schildkraut, Aug 14 2015

STATUS

approved

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Last modified September 22 22:24 EDT 2020. Contains 337291 sequences. (Running on oeis4.)