A176035 Difference between product of two distinct primes and previous perfect square.

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

Offset

1,1

Comments

6-4=2, 10-9=1, 14-9=5, 15-9=6, 21-16=5,..

Links

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

Formula

a(n) = A053186(A006881(n)). - R. J. Mathar, Aug 25 2025

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}] (* Vladimir Joseph Stephan Orlovsky, Jun 02 2011 *)

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

Cf. A006881, A056892, A106044, A176032, A176033, A176034

Sequence in context: A075680 A192024 A249283 * A190992 A160166 A349617

Adjacent sequences: A176032 A176033 A176034 * A176036 A176037 A176038

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Apr 06 2010

Status

approved