A379969 Characteristic function of A239929, numbers k with the property that the symmetric representation of sigma(k) has two parts.

0, 0, 1, 0, 1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 1, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 0, 1, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 1, 0

Offset

1

Links

Antti Karttunen, Table of n, a(n) for n = 1..100000

Index entries for characteristic functions.

Prog

(PARI)
A365429(n) = { my(d=divisors(n)); for(i=2, #d, if(d[i]>2*d[i-1], return(0))); (1); };
A379969(n) = if(1==n, 0, my(f=factor(n), p=f[#f~, 1], q=n/p); ((p > 2*q) && A365429(q))); \\ (after Hartmut F. W. Hoft's Sep 16 2015 comment in A239929)

Crossrefs

Characteristic function of A239929.

Cf. A237593, A365429.

Sequence in context: A358770 A022925 A327211 * A348327 A144607 A327253

Adjacent sequences: A379966 A379967 A379968 * A379970 A379971 A379972

Keyword

nonn

Author

Antti Karttunen, Jan 12 2025

Status

approved