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 A089485 n^4 + 4^n = A001589(n) is a semiprime. 0
 3, 5, 15, 35, 55 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For n = 2*k + 1, n^4 + 4^n = (n^2 + n*2^(k + 1) + 2^n) * (n^2 - n*2^(k + 1) + 2^n) The sequence gives those values of n for which both parentheses are primes. No further terms were found for k<=5000. LINKS Ignacio Larrosa Canestro et al., Find all primes of the form 4^n + n^4. Discussion in newsgroup sci.math. EXAMPLE a(1)=3 because 3^4+4^3=145=5*29, a(2)=5 because 5^4+4^5=1649=17*97. CROSSREFS Cf. A001589. Sequence in context: A148500 A148501 A148502 * A146212 A018516 A138017 Adjacent sequences:  A089482 A089483 A089484 * A089486 A089487 A089488 KEYWORD more,nonn AUTHOR Hugo Pfoertner, Nov 11 2003 STATUS approved

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