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A372564
Positions of -4's in A346242.
2
72, 260, 380, 620, 740, 860, 1220, 1340, 1460, 1580, 1940, 2060, 2180, 2540, 2780, 3020, 3140, 3260, 3620, 3860, 3980, 4220, 4460, 4580, 4820, 5420, 5540, 5660, 6140, 6260, 6620, 6740, 6980, 7340, 7460, 7580, 7940, 8180, 8420, 8660, 8780, 9140, 9260, 9740, 9980, 10460, 10820, 10940, 11420, 11540, 12020, 12140, 12260
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.
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
Cf. also A354814.
Sequence in context: A250749 A019507 A303081 * A158488 A165139 A305222
KEYWORD
nonn
AUTHOR
Antti Karttunen, May 24 2024
STATUS
approved