A172247 - OEIS

A172247

Numbers k for which there are at least 2 partitions k = x+y with x<=y and gcd(x,y,k)=1 having the same value N(x,y,n) defined as the product of distinct prime divisors of x*y*n.

7, 11, 13, 15, 17, 19, 21, 23, 25, 29, 31, 35, 37, 39, 40, 41, 43, 47, 49, 53, 55, 57, 58, 59, 61, 63, 65, 67, 71, 73, 77, 79, 83, 85, 89, 91, 93, 95, 97, 99, 101, 103, 107, 109, 111, 113, 115, 117, 119, 121, 123, 125, 127, 129, 131, 133, 136, 137, 139, 143, 145, 147

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..62.

EXAMPLE

7 is a term because we have two partitions 7=1+6 and 7=3+4 with same value of N(a,b,n) respectively 1*2*3*7=42 and 2*3*7=42.

PROG

(PARI) N(x, y, z) = vecprod(factor(x*y*z)[, 1]);

isok(k) = {my(v = vector(0)); for (x=1, (k-1)\2, my(y = k-x); if (gcd(n, gcd(x, y)) == 1, v = concat(v, N(x, y, k)); ); ); #v != #vecsort(v, , 8); } \\ Michel Marcus, Sep 01 2019

CROSSREFS

Cf. A023022, A172245, A172246, A172248.

Sequence in context: A287161 A051266 A370007 * A374082 A172120 A112090

Adjacent sequences: A172244 A172245 A172246 * A172248 A172249 A172250

KEYWORD

nonn

AUTHOR

Artur Jasinski, Jan 29 2010

EXTENSIONS

Edited by Michel Marcus, Sep 01 2019

STATUS

approved