Jelly, 10 bytes
26RḤ’RØAṁY
How it works
26RḤ’RØAṁY Main link. No Arguments.
26 Set the return value to 26.
R Range; yield [1, 2, ..., 25, 26].
Ḥ Unhalve; yield [2, 4, ..., 50, 52].
’ Decrement; yield [1, 3, ..., 49, 51].
R Range; yield [[1], [1, 2, 3], ..., [1, ..., 49], [1, ..., 51]].
ØA Yield the uppercase alphabet.
ṁ Mold the alphabet as the array of ranges. This repeats the uppercase
letters over an over again, until all integers in the range arrays
have been replaced with letters.
Y Join, separating by linefeeds.
Jelly, 10 bytes
26RḤ’RØAṁY
How it works
26RḤ’RØAṁY Main link. No Arguments.
26 Set the return value to 26.
R Range; yield [1, 2, ..., 25, 26].
Ḥ Unhalve; yield [2, 4, ..., 50, 52].
’ Decrement; yield [1, 3, ..., 49, 51].
R Range; yield [[1], [1, 2, 3], ..., [1, ..., 49], [1, ..., 51]].
ØA Yield the uppercase alphabet.
ṁ Mold the alphabet as the array of ranges. This repeats the uppercase
letters over an over again, until all integers in the range arrays
have been replaced with letters.
Y Join, separating by linefeeds.