R 12 = 1 12 R n−6 + R n+6 2 + ∑ k R k MathType@MTEF@5@5@+= feaagKart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHX garuavP1wzZbItLDhis9wBH5garmWu51MyVXgarqqtubsr4rNCHbGe aGqipG0dh9qqWrVepG0dbbL8F4rqqrVepeea0xe9LqFf0xc9q8qqaq Fn0lXdHiVcFbIOFHK8Feea0dXdar=Jb9hs0dXdHuk9fr=xfr=xfrpe WZqaaeaaciWaamGadaGadeaabaGaaqaaaOqaaiaadkfadaWgaaWcba GaaGymaiaaikdaaeqaaOGaeyypa0ZaaSaaaeaacaaIXaaabaGaaGym aiaaikdaaaWaamWaaeaadaWcaaqaaiaadkfadaWgaaWcbaGaamOBai abgkHiTiaaiAdaaeqaaOGaey4kaSIaamOuamaaBaaaleaacaWGUbGa ey4kaSIaaGOnaaqabaaakeaacaaIYaaaaiabgUcaRmaaqafabaGaam OuamaaBaaaleaacaWGRbaabeaaaeaacaWGRbaabeqdcqGHris5aaGc caGLBbGaayzxaaaaaa@4BF0@
for k = n − 5, n − 4, ..., n, ..., n + 5
where Rk is the mean international relative sunspot number for the kth month