This number is a prime.

                                                    11 2251413721 1631432881

+ The concatenation of the first 4 square triangular numbers with triangular number indexes - squares (1, 1225, 1413721 and 1631432881) is emirp. If we add to these numbers 36 (the second square triangular number) raised respectively to the 1st, 6th, 5th and 6th power (the first 4 digits of the end-digits sequence of the square triangular numbers), we yield four more primes with concatenation - yet another prime. If we add to the initial 4 numbers 1656 (note that it is 81^2 reversed) raised to the power respectively 1, 2, 3 and 4, we yield primes too. [Petrov]

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