OFFSET
1,3
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Bhabesh Das and Helen K. Saikia, On the Sum of Unitary Divisors Maximum Function, AIMS Mathematics, Vol. 2, No. 1 (2017), pp. 96-101.
MATHEMATICA
usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); usigma[1] = 1; a[n_] := Module[{k = n}, While[!Divisible[n, usigma[k]], k--]; k]; Array[a, 100]
PROG
(PARI) usigma(n) = {my(f = factor(n)); prod(i = 1, #f~, 1 + f[i, 1]^f[i, 2]); }
a(n) = {my(k = n); while((n % usigma(k)), k--); k; }
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Aug 06 2024
STATUS
approved