A124141 Numbers k such that there is a number m < k satisfying A000203(k) = A000203(m) = m + k - gcd(m,k).

38, 92, 153, 284, 332, 459, 494, 885, 956, 1035, 1358, 1784, 2295, 2528, 2678, 5434, 5607, 6027, 6255, 7564, 7928, 8235, 8648, 9729, 10325, 10413, 12008, 14104, 15813, 16198, 17794, 22712, 22936, 23247, 27082, 27626, 28917, 30938, 33082, 34688, 37790, 37816

Offset: 1

Author

Yasutoshi Kohmoto, Dec 01 2006

Keywords

• nonn

Examples

			38 is in the sequence because A000203(24) = A000203(38) = 60 = 24 + 38 - gcd(24,38).
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..360
• Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).

Crossrefs

Cf. A000203, A124140.

Subsequence of A069822.

Programs

PARI

isok(k) = {my(sk = sigma(k)); for (m=1, k, if ((sk == sigma(m)) && (sk == m + k - gcd(m,k)), return (1));); return (0);} \\ Michel Marcus, Oct 27 2019

PARI

is(k) = {my(s = sigma(k), v = invsigma(s)); for(i = 1, #v, if(v[i] < k && s == v[i] + k - gcd(v[i], k), return(1))); 0;} \\ Amiram Eldar, Dec 20 2024, using Max Alekseyev's invphi.gp

Extensions

Edited by Stefan Steinerberger, Aug 14 2007

More terms from Jinyuan Wang, Feb 07 2022