A070242 a(n) = Card( k>0 : sigma(k)=sigma(n) ).

1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 3, 3, 2, 2, 1, 1, 3, 2, 1, 3, 3, 2, 3, 1, 2, 1, 5, 2, 1, 3, 2, 3, 1, 1, 3, 2, 3, 3, 4, 1, 3, 1, 5, 3, 2, 1, 1, 5, 2, 2, 4, 5, 4, 2, 3, 3, 6, 1, 4, 2, 1, 3, 5, 1, 2, 4, 5, 5, 1, 1, 2, 2, 2, 4, 6, 2, 2, 1, 2, 3, 3, 2, 2, 4, 4, 3, 3, 1, 6, 2, 5, 4, 6, 2, 1, 2, 1, 1, 5, 2, 2, 5

Offset

1,6

Links

Antti Karttunen, Table of n, a(n) for n = 1..16384

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

Formula

a(n) = A054973(A000203(n)). - Antti Karttunen, Nov 07 2017

Prog

(PARI) for(n=1, 150, print1(sum(i=1, 10*n, if(sigma(n)-sigma(i), 0, 1)), ", "))
(PARI) A070242(n) = { my(s=sigma(n)); length(select(i->sigma(i) == s, vector(s, i, i))); } \\ Antti Karttunen, Nov 07 2017
(PARI) A070242(n) = { my(s=sigma(n)); sum(k=1, s, (sigma(k)==s)); }; \\ Antti Karttunen, Nov 07 2017
(PARI) a(n) = invsigmaNum(sigma(n)); \\ Amiram Eldar, Dec 20 2024, using Max Alekseyev's invphi.gp

Crossrefs

Cf. A000203, A054973, A066412.

Sequence in context: A322870 A170979 A025864 * A242748 A374163 A266012

Adjacent sequences: A070239 A070240 A070241 * A070243 A070244 A070245

Keyword

easy,nonn

Author

Benoit Cloitre, May 09 2002

Status

approved