A190992 Duplicate of A176035.

2, 1, 5, 6, 5, 6, 1, 8, 9, 10, 2, 3, 10, 2, 6, 8, 9, 13, 1, 5, 10, 13, 1, 4, 5, 6, 10, 12, 13, 14, 6, 11, 15, 18, 19, 1, 2, 8, 12, 13, 20, 21, 22, 1, 2, 11, 14, 15, 17, 22, 8, 9, 14, 16, 18, 25, 5, 6, 7, 9, 10, 13, 17, 18, 19, 21, 22, 23, 25, 1, 10, 12, 22, 24, 28, 29, 3, 6, 9, 11, 18, 22, 31, 2

Offset

1,1

Comments

Previous name was: Square excess of squarefree semiprimes.

Links

G. C. Greubel, Table of n, a(n) for n = 1..5000

Mathematica

A006881=Sort@Flatten@Table[Prime[m]*Prime[n], {n, 2, 150}, {m, n-1}];
Table[A006881[[n]]-Floor[Sqrt[A006881[[n]]]]^2, {n, 100}]

Prog

(Magma)
A006881:= [n: n in [1..1000] | EulerPhi(n) + DivisorSigma(1, n) eq 2*(n+1)];
[A006881[n] - Floor(Sqrt(A006881[n]))^2: n in [1..100]]; // G. C. Greubel, Oct 26 2022
(SageMath)
A006881=[n for n in (1..750) if euler_phi(n) + sigma(n, 1) == 2*n+2]
[A006881[n] - isqrt(A006881[n])^2 for n in range(101)] # G. C. Greubel, Oct 26 2022

Crossrefs

Sequence in context: A192024 A249283 A176035 * A160166 A349617 A349616

Adjacent sequences: A190989 A190990 A190991 * A190993 A190994 A190995

Keyword

dead

Author

Vladimir Joseph Stephan Orlovsky, Jun 02 2011

Extensions

Data corrected by G. C. Greubel, Oct 26 2022

Marked as duplicate by R. J. Mathar, Aug 25 2025

Status

approved