groups_get_invited_to_group_ids( int $user_id )

function groups_get_invited_to_group_ids( $user_id = 0 ) {
	if ( empty( $user_id ) ) {
		$user_id = bp_loggedin_user_id();
	}

	$group_ids = groups_get_invites( array(
		'user_id'     => $user_id,
		'invite_sent' => 'sent',
		'fields'      => 'item_ids'
	) );

	return array_unique( $group_ids );
}