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A159829 a(n) is the smallest natural number m such that n^3+m^3+1^3 is prime. 7
1, 2, 1, 2, 1, 4, 15, 2, 3, 2, 11, 10, 9, 2, 7, 14, 5, 4, 9, 2, 15, 2, 7, 16, 15, 8, 13, 2, 1, 10, 3, 4, 15, 2, 11, 10, 9, 2, 7, 6, 13, 22, 5, 2, 1, 6, 29, 10, 29, 10, 3, 2, 11, 12, 3, 8, 3, 2, 19, 6, 15, 8, 1, 2, 1, 18, 5, 2, 1, 18, 1, 12, 17, 14, 15, 26, 7, 6, 3, 2, 19, 12, 1, 18, 3, 8, 15, 2, 11, 6 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

1) a(2k-1) is odd, a(2k) is even.

2) Exponent 2: There are infinitely many primes of the forms n^2+m^2 and n^2+m^2+1^2.

3) Exponent k>2: Are there infinitely many primes of the forms n^k+m^k and n^k+m^k+1^k?

REFERENCES

L. E. Dickson, History of the Theory of Numbers, Vol, I: Divisibility and Primality, AMS Chelsea Publ., 1999

A. Weil, Number theory: an approach through history, Birkhauser 1984

David Wells, Prime Numbers: The Most Mysterious Figures in Math. John Wiley and Sons. 2005

LINKS

Table of n, a(n) for n=1..90.

EXAMPLE

2^3+2^3+1=17 = A000040(7); a(2)=2.

7^3+15^3+1=3719 = A000040(519); a(7)=15.

21^3+15^3+1=18523 = A000040(2122), a(21)=15.

MAPLE

A159829 := proc(n) for m from 1 do if isprime(n^3+m^3+1) then RETURN(m) ; fi; od: end: seq(A159829(n), n=1..120) ; # R. J. Mathar, Apr 28 2009

MATHEMATICA

snn[n_]:=Module[{n3=n^3, m=1}, While[!PrimeQ[n3+1+m^3], m++]; m]; Array[ snn, 100] (* Harvey P. Dale, Sep 04 2019 *)

CROSSREFS

Cf. A069003, A159828

Sequence in context: A295686 A246996 A260612 * A224763 A128515 A119569

Adjacent sequences:  A159826 A159827 A159828 * A159830 A159831 A159832

KEYWORD

nonn

AUTHOR

Ulrich Krug (leuchtfeuer37(AT)gmx.de), Apr 23 2009

EXTENSIONS

Corrected and extended by R. J. Mathar, Apr 28 2009

STATUS

approved

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Last modified November 22 16:31 EST 2019. Contains 329396 sequences. (Running on oeis4.)