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A114973 Numbers n such that 5^n + n^5 is a semiprime. 4
1, 2, 4, 6, 8, 9, 84, 288, 628 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(10) >= 868. - Hugo Pfoertner, Jul 28 2019

LINKS

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

Status of 5^868-868^5 in factordb.com.

EXAMPLE

2 is OK because 5^2 + 2^5 = 25 + 32 = 57 = 3*19 (semiprime).

MATHEMATICA

Select[Range[100], PrimeOmega[5^# + #^5]==2&] (* Vincenzo Librandi, May 21 2014 *)

PROG

(MAGMA)IsSemiprime:=func< n|&+[k[2]: k in Factorization(n)] eq 2 >; [n: n in [1..85]|IsSemiprime(5^n+n^5)]; // Vincenzo Librandi, Dec 16 2010

CROSSREFS

Cf. A094133, A114970, A114971, A114974.

Sequence in context: A080223 A156759 A276138 * A004522 A004521 A103694

Adjacent sequences:  A114970 A114971 A114972 * A114974 A114975 A114976

KEYWORD

nonn,more,hard

AUTHOR

Zak Seidov, Feb 22 2006

EXTENSIONS

a(8), a(9) from Hugo Pfoertner, Jul 28 2019

STATUS

approved

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Last modified June 5 18:48 EDT 2020. Contains 334854 sequences. (Running on oeis4.)