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A252790 Numbers m such that 5^m + m is a semiprime. 1
1, 4, 8, 17, 144, 154, 298 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(8) > 413. - Carl Schildkraut, Aug 14 2015

LINKS

Table of n, a(n) for n=1..7.

EXAMPLE

1 is in this sequence because 5^1+1 = 2*3 is semiprime.

8 is in this sequence because 5^8+8 = 3*130211 and these two factors are prime.

MATHEMATICA

Select[Range[413], PrimeOmega[5^# + #]==2 &]

PROG

(MAGMA) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..110] | IsSemiprime(s) where s is 5^m+m];

(PARI) main(m)=select(m->bigomega(5^m + m)==2, vector(m, i, i)); \\ Anders Hellström, Aug 14 2015

CROSSREFS

Cf. similar sequences listed in A252788.

Cf. A252658.

Sequence in context: A296399 A119471 A145779 * A144178 A075558 A312824

Adjacent sequences:  A252787 A252788 A252789 * A252791 A252792 A252793

KEYWORD

nonn,more

AUTHOR

Vincenzo Librandi, Dec 24 2014

EXTENSIONS

a(5)-a(7) from Carl Schildkraut, Aug 14 2015

STATUS

approved

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Last modified September 25 12:57 EDT 2021. Contains 347654 sequences. (Running on oeis4.)