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COMMENTS
| a(2) is prime. a(4) is prime, as pointed out by Poo Sung on Prime Curios for 331997. a(3), a(5) and a(11) are semiprime. a(6), a(7), a(8) and a(10) have 3 prime factors. a(9) has 7 prime factors. a(12) has at least 4 prime factors. From a(4) onwards, all terms are congruent to 31997 mod 10^5. From a(5) onwards, all terms are congruent to 531997 mod 10^6. From a(5) onwards, all terms are congruent to 7531997 mod 10^7. The number of digits of a(n) for n = 1, 2, 3, ..., 12 are 1, 1, 3, 6, 11, 18, 26, 37, 51, 84, 105.
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EXAMPLE
| a(1) = (1!)^1 = 1^1 = 1.
a(2) = (1!)^1 + (2!)^2 = 1^1 + 2^2 = 1 + 4 = 5.
a(3) = (1!)^1 + (2!)^2 + (3!)^3 = 1^1 + 2^2 + 6^3 = 1 + 4 + 216 = 221.
a(4) = (1!)^1 + (2!)^2 + (3!)^3 + (4!)^4 = 1^1 + 2^2 + 6^3 + 24^4 = 1 + 4 + 216 + 331776 = 331997.
a(10) = (1!)^1 + (2!)^2 + (3!)^3 + (4!)^4 + (5!)^5 + (6!)^6 + (7!)^7 + (8!)^8 + (9!)^9 + (10!)^10.
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