A347863 Odd terms in A015782.

7, 21, 93, 357, 381, 681, 1541, 7181, 24573, 36893, 192061, 388669, 393213, 1505533, 1572861, 10678781, 24736253

Offset

1,1

Comments

Odd numbers n such that phi(n)+3 divides sigma(n+3), where phi = A000010 and sigma = A000203.

Links

Table of n, a(n) for n=1..17.

Example

a(3) = 93 is a term because phi(93)+3 = 63 divides sigma(96) = 252 = 4*63.

Maple

filter:= proc(n) uses numtheory;
   sigma(n+3) mod (3+phi(n)) = 0
end proc:
select(filter, [seq(i, i=1..2*10^6, 2)]);

Mathematica

Select[Range[1, 2*10^6, 2], Divisible[DivisorSigma[1, # + 3], EulerPhi[#] + 3] &] (* Amiram Eldar, Jan 24 2022 *)

Crossrefs

Cf. A000010, A000203, A015782.

Sequence in context: A164544 A100025 A121157 * A253072 A261854 A219152

Adjacent sequences: A347860 A347861 A347862 * A347864 A347865 A347866

Keyword

nonn,more

Author

Robert Israel, Jan 24 2022

Extensions

a(16)-a(17) from Amiram Eldar, Jan 24 2022

Status

approved