Since the numbers begin with 123, they all contain a 3. As a result, they all "contain 3 or 7".
So the remaining 4 digits can be any digits and this gives 104 = 10,000 such numbers.
Benin is country code +229. The rest of the number is 8 further digits. Landline numbers begin with +229 2. Mobile numbers begin with +229 9.
Uzbekistan is country code +998. All numbers have 9 digits after country code +998. Mobile numbers begin with +998 9.
The telephone country code for Australian research bases in Antarctica is +672. Numbers in the Macquarie base begin with +672 139, with a further three digits.
The telephone country code for Australian research bases in Antarctica is +672. Numbers in the Casey base begin with +672 128, with a further three digits.
The telephone country code for Australian research bases in Antarctica is +672. Numbers in the Davis base begin with +672 106, with a further three digits.
The telephone country code for Australian research bases in Antarctica is +672. Numbers in the Mawson base begin with +672 117, with a further three digits.
Djibouti is country code +253. Landlines in the city of Djibouti begin with +253 21. Landlines in the outer districts begin with +253 27. Mobile numbers begin with +253 77. All numbers have 8 digits following the country code +253. Note that all telephone numbers in Djibouti changed in March 2012. See the related links for details.
Macau is country code +853. There are no area codes within Macau. Most numbers are 8 digits after the country code +853. Most ordinary landline numbers begin with +853 2. Direct dial-in numbers begin with +853 8. Most mobile numbers begin with +853 6.
Credit cards have a series of 14-16 digits, beginning with the numbers 3, 4, 5 or 6. American Express cards begin with 3 and have 15 digits. Diners Club and Carte Blanche (JCB) cards begin with 3 and have 14 or 16 digits. Visa cards begin with 4 and have 16 digits. (Old cards used to have 14 digits). Mastercard cards begin with 5 and have 16 digits. Discover cards begin with 6 (usually 6011) and have 16 digits.
El Salvador is country code +503. There are no city codes or area codes. Landline numbers begin with +503 2. Mobile numbers begin with +503 6 or +503 7. The local number is 8 digits, except for freephone and premium-rate numbers.
The Maldives use country code +960. There are no city codes or area codes. All numbers are 7 digits after the country code. Landlines in the Male region begin with +960 3. Landlines in the atolls begin with +960 6. Mobile numbers begin with +960 7 (Dhiraagu) or +960 9 (Wataniya Telecom). There are also premium-rate numbers beginning with +960 900, followed by 7 additional digits.
Toll-free numbers in India begin with 1800.