2,1

The earliest chain of 4 consecutive primes separated by gaps 2^1, 2^2, 2^3 is:

1997, 1999, 2003, 2011. Hence a(4) = 1997.

Sequence in context: A119497 A012783 A062655 this_sequence A167483 A138154 A126334

Adjacent sequences: A090804 A090805 A090806 this_sequence A090808 A090809 A090810

nonn

Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Feb 12 2004