A350086 a(n) is the smallest totient number k > 1 such that A005277(n)*k is a nontotient number, or 0 if no such number exists.

22, 22, 2, 2, 22, 2, 10, 10, 2, 6, 106, 2, 22, 46, 2, 2, 2, 6, 2, 10, 2, 2, 6, 2, 78, 2, 18, 2, 6, 2, 2, 2, 2, 46, 58, 2, 2, 2, 58, 2, 6, 2, 2, 2, 10, 10, 2, 46, 2, 2, 2, 82, 2, 30, 2, 6, 2, 10, 2, 10, 46, 2, 2, 2, 2, 2, 6, 78, 2, 10, 2, 10, 46, 10, 2, 46, 2

Offset: 1

Author

Jianing Song, Dec 12 2021

Keywords

• nonn

Comments

Subsequence of A350085.

Conjecture: a(n) != 0 for all n.

Records: 22 (A005277(n) = 14), 106 (A005277(n) = 90), 2010 (A005277(n) = 450), ...

By definition, a totient number N > 1 is a term if and only if there exists an even nontotient r such that: (i) k*r is a totient for totient numbers 2 <= k < N; (ii) N*r is a nontotient. No term can be of the form m*m', where m > 1 is a totient and m' > 1 is in A301587 (otherwise m*r is a totient implies m*m'*r is a totient).

Conjecture: every totient number > 1 which is not of the form m*m', where m > 1 is a totient and m' > 1 is in A301587, appears in this sequence. For example, the numbers 2, 6, 10, 18, 22, 28, 30 first appears when A007617(n) = 7, 15, 5, 33, 11, 902, 3.

Examples

			A005277(11) = 90. N = 106 is a totient number > 1 such that 90*k is a totient for totient numbers 2 <= k < N, and 90*N is a nontotient, so a(11) = 106.
A005277(83) = 450. N = 2010 is a totient number > 1 such that 450*k is a totient for totient numbers 2 <= k < N, and 450*N is a nontotient, so a(83) = 2010.
A005277(187) = 902. N = 28 is a totient number > 1 such that 902*k is a totient for totient numbers 2 <= k < N, and 902*N is a nontotient, so a(187) = 28.
A005277(73991) = 241010. N = 100 is a totient number > 1 such that 241010*k is a totient for totient numbers 2 <= k < N, and 241010*N is a nontotient, so a(73991) = 100. Note that although 100 = 10*10 is a product of 2 totient number > 1, neither factor is in A301587, so nothing prevents that 100 is a term of this sequence.
		

Links

• Michel Marcus, Table of n, a(n) for n = 1..8458

Crossrefs

Cf. A005277, A350085, A301587.

Programs

PARI

b(n) = if(!istotient(n), for(k=2, oo, if(istotient(k) && !istotient(n*k), return(k))))
list(lim) = my(v=[]); forstep(n=2, lim, 2, if(!istotient(n), v=concat(v,b(n)))); v \\ gives a(n) for A005277(n) <= lim