A358022
Least odd number m such that m*2^n is an amicable number, and -1 if no such number exists.
Original entry on oeis.org
12285, 605, 55, 779, 1081, 37, 119957, 73153, 2927269, 239, 25329329, 7230607, 964119281, 66445153, 7613527, 18431675687, 328796066369, 264003743, 11298797322497, 59592560831, 949755039781, 2759891672513
Offset: 0
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f(m) = if (m, sigma(m)-m, 0);
fpm(p, m) = (2*p-1)*sigma(m) - p*m;
a(n) = my(p=2^n); forstep(m=1, +oo, 2, my(x=fpm(p,m)); if ((x!=p*m) && (f(x) == p*m), return(m)));
a(12)-a(22) were calculated using Chernykh's database by
Amiram Eldar, Nov 17 2022
A358546
Least odd number m such that m mod 3 > 0 and m*3^n is an amicable number, and -1 if no such number exists.
Original entry on oeis.org
5480828320492525, 4865, 7735, 455, 131285, 849355, 11689795, 286385, 187047685, 104255, 32851039955, 2085985, 47942199242945, 189296520259, 349700961302721360788238344333849, 580068028631, 50392682631679406080371010751466781
Offset: 0
a(1) = 4865, because 4865 is an odd number and 4865 % 3 > 0 and 4865 * 3 = 14595 is an amicable number, and no lesser number has this property.
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sigmap(k)=if(k,sigma(k)-k,0)
cycle(k, TT=2)=my(x=k, T=1); while(x>0&&T<=TT, x=sigmap(x); if(x==k, return(T)); T++)
a(n, TT=2)=my(p3n=3^n); forstep(m=1, +oo, 2, if(m%3&&cycle(p3n*m, TT)==2, return(m)))
Showing 1-2 of 2 results.
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