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lucky numberstresses
math. счастливое число (In number theory, a lucky number is a natural number in a set which is generated by a "sieve" similar to the Sieve of Eratosthenes that generates the primes. The lucky numbers are 1, 3, 7, 9, 13, 15, 21, 25, 31, 33, 37, 43, 49, 51, 63, 67, 69, 73, 75, 79, 87, 93, 99, ... . The term was introduced in 1955 in a paper by Gardiner, Lazarus, Metropolis and Ulam Alex_Odeychuk)
lucky number: 2 phrases in 2 subjects
Idiomatic1
Makarov1