Merge group numbers and add a column containing group names

Hi All
I do have a file like this with 6 columns. Groups of data merge together and the group number is indicated above each group.

1
1       12      26      289     3.2e-027        GCGTATGGCGGC
2       12      26      215     6.7e+006        TTCCACCTTTTG
3       9       26      175     8.9e+016        GCGGTAACT
4       20      26      232     1.7e+013        TTTTTATTTTTTTTTTTTCC
5       7       26      161     7.2e+019        ATGCAAA
6       7       26      161     4.2e+019        CTTCAAA
7       7       26      144     7.4e+025        AGAAAAA
8       7       26      155     2.6e+021        TAGGCTG
9       9       26      148     7.3e+028        AATTTATTC
10      7       26      156     1.8e+021        TTGATTT
2
1       16      37      404     2.3e-025        AAAATTGCATGCATGC
2       12      37      351     6.1e-009        AAGAAAAAAAAA
3       9       37      328     1.5e-007        TTTGCCGCC
4       20      37      369     1.2e+001        AAAAGAGGAAAAAAAAAAAA
5       9       37      295     3.1e+007        ATGCATGTA
6       9       37      280     3.3e+014        CATTTTTTT
7       16      37      313     6.1e+015        AGAGAAAAATTAAAAA
8       11      37      288     7.5e+015        AATAATTTGAG
9       7       37      247     4.5e+023        GGAAAGG
4       20      37      369     1.2e+001        AAAAGAGGAAAAAAAAAAAA
3
1       11      36      329     6.0e-012        ATTTGCATGCA
2       7       36      277     7.0e+001        GTGGGGA
3       9       36      273     3.9e+008        CTTACATGC
4       12      36      287     7.1e+010        AAAAAAAGTAAA
5       9       36      254     1.9e+017        ATTTGGCGA
6       7       36      228     6.7e+023        TCCCTTC
7       12      36      255     2.8e+024        TAATAATTTATT
8       16      36      252     5.6e+032        TTTTAAAGAATAATCA
9       16      36      228     1.3e+042        TTTTTTCTGTATTATT
10      12      36      224     5.1e+035        CCACATAAAAAT
.
.
.
.

150
1       7       11      102     7.0e-001        CCCGCCA
2       7       11      90      2.0e+005        GCACTTT
3       12      11      108     7.0e+004        CCCCCAACAATA
4       9       11      94      3.4e+007        GATTTGGAA
5       7       11      87      1.1e+007        AAGAGCT
6       9       11      91      2.1e+009        ATTAAGTTT
7       7       11      84      7.0e+007        CTGGTCA
8       12      11      100     4.4e+009        TTTATTAATCAT
9       7       11      77      3.0e+011        ATTTATG
10      12      11      90      1.7e+013        CATTTTTTTTAC

I wanted to add another column (separated by tab) such that the file looks like:

1 1       12      26      289     3.2e-027        GCGTATGGCGGC
 1 2       12      26      215     6.7e+006        TTCCACCTTTTG
 1 3       9       26      175     8.9e+016        GCGGTAACT
 1 4       20      26      232     1.7e+013        TTTTTATTTTTTTTTTTTCC
 1 5       7       26      161     7.2e+019        ATGCAAA
1       16      37      404     2.3e-025        AAAATTGCATGCATGC
 2 2       12      37      351     6.1e-009        AAGAAAAAAAAA
 2 3       9       37      328     1.5e-007        TTTGCCGCC
 2 4       20      37      369     1.2e+001        AAAAGAGGAAAAAAAAAAAA
 2 5       9       37      295     3.1e+007        ATGCATGTA
 2 6       9       37      280     3.3e+014        CATTTTTTT
.
.
.
.
150 1       7       11      102     7.0e-001        CCCGCCA
 150 2       7       11      90      2.0e+005        GCACTTT
 150 3       12      11      108     7.0e+004        CCCCCAACAATA
 150 4       9       11      94      3.4e+007        GATTTGGAA
 150 5       7       11      87      1.1e+007        AAGAGCT

Basically add a column that contains the number of each group and delete the group heading and merge.

Is there an efficient way using shell scripting to do it. I have 1000's of such small groups to manipulate.

Please let me know.

LA

awk 'NF==1{o=$1;next}$0=o"\t"$0' infile