cp_library/math/series/mod/arthsum_fn.py

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• Last update: 2025-03-30 20:17:47+09:00

Code

import cp_library.math.series.__header__

def arthsum(d, a, n, mod):
    return (((n-1)*d+(a<<1)) % mod * n >> 1) % mod

'''
╺━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━╸
             https://kobejean.github.io/cp-library               
'''

def arthsum(d, a, n, mod):
    return (((n-1)*d+(a<<1)) % mod * n >> 1) % mod

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