A370682 Numbers k such that A370681(k) = A370681(k+1).

1, 5, 11, 19, 71, 203, 271, 979, 991, 2755, 5976, 6407, 7004, 8560, 9143, 33552, 46583, 75856, 87955, 90287, 101955, 243271, 265587, 269648, 457135, 510192, 512783, 551172, 559656, 1804555, 1917639, 2902175, 4339952, 6783820, 9842748, 10463980, 17428447, 21677503

Offset: 1

Author

Amiram Eldar, Feb 26 2024

Keywords

• nonn

Examples

			5 is a term since A370681(5) = A370681(6) = 4.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..120

Crossrefs

Cf. A064125, A333261, A370681.

Programs

Mathematica

s[n_] := Module[{d = Reverse[Select[Divisors[n], CoprimeQ[#, n/#] &]]}, Total[(-1)^(Range[Length[d]] + 1)*d]]; Select[Range[10^5], s[#] == s[# + 1] &]

PARI

s(n) = {my(d = Vecrev(select(x->(gcd(x, n/x) == 1), divisors(n)))); sum(i=1, #d, (-1)^(i+1)*d[i]);}
lista(nmax) = {my(s1 = s(1), s2); for(n = 2, nmax, s2 = s(n); if(s1 == s2, print1(n-1,", ")); s1=s2);}