A347863 - OEIS

A347863

Odd terms in A015782.

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

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OFFSET

1,1

COMMENTS

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

LINKS

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

KEYWORD

nonn,more

AUTHOR

EXTENSIONS

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

STATUS

approved