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A077759
Smaller of the two successive triangular numbers which differ in the use of only one digit.
0
0, 1, 3, 10, 15, 21, 45, 105, 136, 190, 210, 231, 325, 435, 465, 780, 1081, 1225, 1485, 1596, 2415, 3081, 4005, 4465, 4560, 5253, 6670, 7021, 7750, 9730, 14365, 15576, 16653, 17020, 19306, 20100, 20301, 23436, 24310, 24531, 30135, 30628, 36585
OFFSET
1,3
COMMENTS
The i-th triangular number T(i) is in the sequence if and only if its successor T(i+1) can be obtained by changing a single digit of T(i) and, if necessary, changing the order of the digits. Thus the sequence does not include 55, even though it and its successor 66 could be said to "differ in the use of only one digit" (i.e., using 5 vs. using 6). Triangular numbers such as 404550, whose successor 405450 uses the same digits in the same frequencies, would also be excluded. - Jon E. Schoenfield, Sep 05 2009
EXAMPLE
231 belongs to this sequence as 231 and 253 differ in the use of only one digit, i.e., 1 and 5.
CROSSREFS
Sequence in context: A108770 A112355 A074314 * A278291 A247420 A063231
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Nov 21 2002
EXTENSIONS
More terms from Jon E. Schoenfield, Sep 05 2009
STATUS
approved