A147803 Least m coprime to 5 minimizing A007947(m*(5^n-m)).

1, 1, 4, 49, 128, 9, 36864, 19332, 4508, 121, 2

Offset: 1

Author

M. F. Hasler, Nov 13 2008

Keywords

• nonn
• more

Comments

The minima are given in A147800.

This is related to the abc conjecture: Since m is coprime to 5, it is also coprime to 5^n and thus to 5^n-m. Thus the squarefree kernel A007947(m*(5^n-m)*5^n) = 5*A007947(m*(5^n-m)).

Crossrefs

Cf. A007947, A147298 (general case), A147800 (value of minima), A143700 (analog for 2^n), A147802 (analog for 3^n), A147300 (analog for any number).

Programs

PARI

A147803(n,p=5) = {my(b, m=n=p^n); for(a=1, n\2, a%p || next; A007947(n-a)*A007947(a)A007947((n-a)*b=a)); b; }