OFFSET
1,1
COMMENTS
Term a(94)=23256 is the first term after 72 that is not a multiple of 20. The first four odd terms 71825, 942667, 1322035, 3613027 occur at indices n=273, 3355, 4619, 11995.
Of the first 20000 terms, 13422 are multiples of 20, and apparently, for any n > 1, 20*A002476(n) is included in this sequence.
LINKS
PROG
(PARI)
A324198(n) = { my(m=1, p=2, orgn=n); while(n, m *= (p^min(n%p, valuation(orgn, p))); n = n\p; p = nextprime(1+p)); (m); };
memoA346242 = Map();
A346242(n) = if(1==n, 1, my(v); if(mapisdefined(memoA346242, n, &v), v, v = -sumdiv(n, d, if(d<n, A324198(n/d)*A346242(d), 0)); mapput(memoA346242, n, v); (v)));
isA372564(n) = (-4==A346242(n));
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, May 24 2024
STATUS
approved