A069822 Numbers k for which there is at least one x < k such that sigma(x) = sigma(k).

11, 15, 17, 23, 25, 26, 31, 35, 38, 39, 41, 46, 47, 51, 53, 55, 56, 58, 59, 62, 65, 69, 70, 71, 75, 77, 78, 79, 82, 83, 87, 89, 92, 94, 95, 97, 103, 107, 110, 113, 115, 116, 118, 119, 122, 123, 124, 125, 127, 130, 131, 135, 139, 140, 141, 142, 143, 145, 151, 153

Offset

1,1

Comments

Numbers k for which A263025(k) > 1. - Antti Karttunen, Dec 08 2017

Links

Antti Karttunen, Table of n, a(n) for n = 1..10547

Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).

Prog

(PARI) for(s=1, 200, if(prod(i=1, s-1, sigma(i)-sigma(s))==0, print1(s, ", ")))
(PARI) for(n=1, 16384, y=0; s=sigma(n); for(k=1, (n-1), if(sigma(k)==s, y=1; break)); if(y, i++; write("b069822.txt", i, " ", n))); \\ Antti Karttunen, Dec 08 2017
(PARI) is(k) = invsigmaMin(sigma(k)) < k; \\ Amiram Eldar, Dec 20 2024, using Max Alekseyev's invphi.gp

Crossrefs

Cf. A263025, A296214.

Cf. A296087 (a subsequence).

Sequence in context: A365329 A186404 A111322 * A116999 A309362 A279422

Adjacent sequences: A069819 A069820 A069821 * A069823 A069824 A069825

Keyword

easy,nonn,changed

Author

Benoit Cloitre, Apr 28 2002

Status

approved