A347390 Odd numbers k that can be factored to such a pair of coprime factors x and y that A347381(k) < min(A347381(x), A347381(y)).

189, 455, 945, 1271, 1365, 2125, 4199, 6375, 9261, 12597, 13167, 15631, 18189, 20995, 21275, 24583, 26273, 29393, 30879, 42813, 43475, 46163, 46189, 46305, 46575, 46893, 54653, 63767, 63825, 65317, 67473, 67673, 73749, 78155, 78725, 89503, 90117, 90945, 92783, 93869, 106079, 108819, 119239, 122265, 127323, 129575

Offset: 1

Author

Antti Karttunen, Sep 09 2021

Keywords

• nonn

Examples

			189 is a term, because A347381(189) = 1, and 189 can be factored as 7*27 with gcd(7,27)=1, and A347381(7) = A347381(27) = 3 > 1.
455 is a term, because A347381(455) = 2, and 455 can be factored as 7*65 with gcd(7,65)=1, and A347381(65) = 4 > A347381(7) = 3 > A347381(455) = 2.
945 is a term, because A347381(945) = 1, and 945 can be factored as 27*35 with gcd(27,35)=1, and A347381(27) = 3 > A347381(35) = 2 > A347381(945) = 1.
1542968918569 = (13*19*47*107)^2 is a term, because it can be factored as 893^2 * 1391^2, with gcd(893^2, 1391^2) = 1, and A347381(1391^2) = 30 > A347381(893^2) = 17 > A347381(1542968918569) = 12. (This is probably the smallest square present in the sequence).
		

Links

• Index entries for sequences computed from indices in prime factorization
• Index entries for sequences related to sigma(n)

Crossrefs

Cf. A347381, A347391.

Subsequence of A347384. Cf. also A347383 (subsequence).

Programs

PARI

isA347390(n) = if(!(n%2),0,my(w=A347381(n)); fordiv(n,d,if(d>(n/d),return(0)); if(1==gcd(d,n/d) && (min(A347381(d),A347381(n/d))>w), return(1))); (0));