"Number of Aadhaar letters issued to transgenders is 19,447," the UIDAI said in reply to an RTI query.
Nearly 16 crore such numbers have been issued to various individuals since the inception of the authority in 2009.
Of the total of 15,98,86,247 cards, a total of 7,71,158 were issued in 2010, 10,21,09,536 in 2011 and 3,40,02,219 were issued between January and February this year, it said.
UIDAI is mandated to issue every citizen a 12-digit unique identification number linked to the resident's demographic and biometric information, which they can use to identify themselves anywhere in India, and to access a host of benefits and services.
The authority, which acts as an attached office of the Planning Commission, was set up in January 28, 2009.
According to the reply, the UIDAI is facing a manpower crunch as about 45 per cent of its total sanctioned strength of 383 are lying vacant.
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"The total sanctioned strength of UIDAI is 383, out of this 204 officers or staff are in place. Appointment for remaining vacancies is in progress," the reply said.
Vacancies exists almost at all the levels including the post of additional directors general, deputy directors, section officers, office assistants and other supporting staff at both its headquarters in Delhi and regional offices.
The reply said that government had made budget estimates of Rs 1,300 crore for UIDAI during 2012-13. The authority has received Rs 120 crore during 2009-10, Rs 1,900 in 2010-11 and Rs 1,470 crore during 2011-12.