A053474 -id:A053474 - cp's OEIS frontend

A053568 Totients of nontotient numbers.

2, 4, 6, 6, 10, 12, 6, 8, 16, 18, 12, 22, 20, 12, 18, 28, 30, 20, 16, 24, 36, 18, 24, 40, 42, 24, 46, 42, 20, 32, 52, 40, 36, 58, 60, 30, 36, 48, 66, 32, 44, 70, 72, 36, 40, 36, 60, 78, 54, 82, 64, 42, 56, 88, 24, 72, 60, 46, 72, 96, 42, 60, 100, 102, 48, 106

Offset: 1

Labos Elemer, Jan 17 2000

nonn

See comment at analogous sequence A053474.

			If k = 19 then there is no number x such that phi(x) = k exists; however, phi(19) = 18.
k = 27 is also a nontotient number whose totient is 18.

Amiram Eldar, Table of n, a(n) for n = 1..10000

Cf. A000010, A007617, A053474.

lista(nn) = for (n=1, nn, if (!istotient(n), print1(eulerphi(n), ", "))); \\ Michel Marcus, Nov 20 2017

a(n) = A000010(A007617(n)).

A053569 Sum of divisors of numbers which cannot be sum of divisors of any number.

Original entry on oeis.org

3, 6, 13, 18, 12, 31, 18, 20, 32, 36, 24, 31, 42, 40, 30, 48, 54, 48, 38, 42, 44, 78, 72, 48, 57, 93, 72, 98, 54, 72, 90, 60, 62, 127, 84, 144, 68, 96, 144, 72, 74, 124, 140, 96, 80, 121, 126, 84, 108, 132, 120, 180, 90, 168, 144, 120, 98, 156, 217, 102, 104, 192, 162

Offset: 1

Labos Elemer, Jan 17 2000

nonn

See also comments in A053474.

			The 13th non-sigma number is 26. Its divisors are {26,13,2,1} of which the sum is 42. So a(13) = 42.
Also a(20) = 42, the divisor sum of 20th term in A007369, which is 41.

Amiram Eldar, Table of n, a(n) for n = 1..10000

Cf. A000203, A007369, A053474.

a(n) = A000203(A007369(n)).

cp's OEIS Frontend

A053568 Totients of nontotient numbers.

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