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A139294
2^(2p - 1), where p is a Mersenne prime A000668(n).
19
32, 8192, 2305843009213693952, 14474011154664524427946373126085988481658748083205070504932198000989141204992
OFFSET
1,1
COMMENTS
Next terms have 4932, 78913, 315652, 1292913986, and 1388255822130839283 decimal digits. - Jens Kruse Andersen, Jul 14 2014
FORMULA
a(n) = 2^(2*A000668(n)-1).
MATHEMATICA
A000668 := Select[2^Range[500] - 1, PrimeQ]; Table[2^(2*A000668[[n]] - 1), {n, 1, 5}] (* G. C. Greubel, Oct 03 2017 *)
PROG
(PARI) \p 100
print1("a(n): "); forprime(q=2, 7, p=2^q-1; if(isprime(p), print1(2^(2*p-1)", ")));
print1("\nNumber of digits in a(n): "); forprime(q=2, 127, p=2^q-1; if(isprime(p), print1(ceil((2*p-1)*log(2)/log(10))", "))) \\ Jens Kruse Andersen, Jul 14 2014
KEYWORD
nonn
AUTHOR
Omar E. Pol, Apr 13 2008
STATUS
approved