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A252795
Numbers m such that 10^m + m is a semiprime.
1
3, 7, 37, 43, 49, 51, 57, 73, 127
OFFSET
1,1
COMMENTS
a(10) >= 217. - Hugo Pfoertner, Aug 06 2019
574 and 601 are also terms in this sequence. - Kevin P. Thompson, May 02 2022
EXAMPLE
3 is in this sequence because 10^3+3 = 17*59 is semiprime.
7 is in this sequence because 10^7+7 = 941*10627 and these two factors are prime.
MATHEMATICA
Select[Range[70], PrimeOmega[10^# + #]==2 &]
PROG
(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..70] | IsSemiprime(s) where s is 10^m+m];
(PARI) is(n)=bigomega(10^n + n)==2 \\ Anders Hellström, Aug 15 2015
CROSSREFS
Cf. similar sequences listed in A252788.
Sequence in context: A269995 A281093 A199347 * A049493 A260380 A363667
KEYWORD
nonn,more,hard
AUTHOR
Vincenzo Librandi, Dec 27 2014
EXTENSIONS
a(8) from Carl Schildkraut, Aug 15 2015
Missing a(8) term added by Kevin P. Thompson, May 02 2022
STATUS
approved