Rav Chayim Palachi (Turkey, 1788-1868), in his work Mo'ed Le'kol Chai (8), records the custom to give charity on Erev Shavuot. One should set aside ninety-one coins (whichever coins one chooses) and then add another thirteen coins one at a time, until he reaches a total of 104, twice the numerical value of the Hebrew word "Ben" ("son"). One should then give the money to a needy Torah scholar.
Rav Chayim Palachi adds that this practice is effective in earning atonement for the sin of Adam in Gan Eden, the sin of the golden calf, and sins involving the desecration of the Berit Mila. Moreover, it functions as a "Segula" to help childless couples have children, and to bring the redemption closer.