A080472 a(n) = smallest triangular number that is obtained by placing digits anywhere in n; a(n) = n if n is a triangular number.
1, 21, 3, 45, 15, 6, 78, 28, 91, 10, 171, 120, 136, 1431, 15, 136, 171, 1081, 190, 120, 21, 1225, 231, 2145, 253, 276, 276, 28, 2926, 300, 231, 325, 3003, 2346, 325, 36, 378, 378, 3916, 406, 741, 4278, 435, 4465, 45, 406, 4278, 1485, 496, 1540, 351, 528, 153, 1540
Offset: 1
Links
- Michael S. Branicky, Table of n, a(n) for n = 1..10000
Programs
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Python
from math import isqrt from itertools import count def dmo(n, t): if t < n: return False while n and t: if n%10 == t%10: n //= 10 t //= 10 return n == 0 def a(n): return next(t for t in (i*(i+1)//2 for i in count(isqrt(2*n))) if dmo(n, t)) print([a(n) for n in range(1, 77)]) # Michael S. Branicky, Jan 21 2023
Extensions
More terms from Ray Chandler, Oct 11 2003