Industrial and Commercial Bank of China (ICBC) aims to raise 21 billion US dollars in what would be the world's biggest IPO in a dual Hong Kong and Shanghai listing in October, Reuters reported, citing a source familiar with the situation on Monday.   The dual offering, which would be the first simultaneous Hong Kong and mainland China listing, is on track to surpass Japan's NTT Mobile Communications, which raised 18.4 billion US dollars in 1998, as the largest-ever initial public offering.   The deal, arranged by Credit Suisse, Deutsche Bank, Merrill Lynch, ICEA, and a consortium led by China International Capital Corp. (CICC) that includes Morgan Stanley would value ICBC at around 116 billion US dollars, ranking it the world's number-six lender after JPMorgan Chase & Co, according to Reuters.   The offering would also outshine the Bank of China which raised US$11.2 billion in Hong Kong in late May, and subsequently raised 20 billion yuan in a Shanghai listing earlier this month, Reuters wrote.