A151991 - OEIS

A151991

Numbers k with the property that (k-x)*(k-y)*(k-z) = x*y*z has no integer solutions 0 < x,y,z < k.

1, 3, 5, 7, 9, 11, 13, 17, 19, 21, 23, 25, 27, 29, 31, 33, 37, 39, 41, 43, 47, 49, 51, 53, 57, 59, 61, 67, 69, 71, 73, 79, 81, 83, 87, 89, 93, 95, 97, 101, 103, 107, 109, 111, 113, 115, 121, 123, 125, 127, 129, 131, 133, 137, 139, 141, 145, 147, 149, 151, 155, 157, 159

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OFFSET

1,2

COMMENTS

All odd primes are terms of this sequence.

LINKS

Table of n, a(n) for n=1..63.

EXAMPLE

15 is not a term of this sequence because (15-x)*(15-y)*(15-z) = x*y*z has the solution (5,5,12).

PROG

(Python)

def exis(n):

for x in range(1, n):

for y in range(x+1):

for z in range(y+1):

if x*y*z==(k-x)*(k-y)*(k-z):

return True

return False

for k in range(1, 200, 2):

if not exis(k):

print(str(k), end=', ')

(PARI) is(n)=for(x=1, n-1, for(y=1, x, my(t=(n-x)*(n-y), z=t*n/(x*y+t)); if(denominator(z)==1 && 0 < z && z < n, return(0)))); 1 \\ Charles R Greathouse IV, Dec 09 2014

CROSSREFS

Cf. A065091 (odd primes).

Sequence in context: A324761 A356171 A244579 * A360114 A265166 A366251

Adjacent sequences: A151988 A151989 A151990 * A151992 A151993 A151994

KEYWORD

nonn

AUTHOR

Nurdin Takenov (greanvert(AT)gmail.com), Sep 14 2009

EXTENSIONS

Edited by Charles R Greathouse IV, Dec 09 2014

STATUS

approved