Friendly Number Calculator
Free online friendly number calculator. Enter your values and get instant results with the formula, step-by-step working, a worked example and FAQs — everything runs locally in your browser on Calcton, no signup required.
中文版：友好数在线计算器
经典示例
I(30) = I(140) = I(2480) = 12/5；I(80) = I(200) = 93/40；所有完全数 I = 2
丰度指数（abundancy index）衡量「数的饱和度」：完全数恰为 2，丰数大于 2。两个完全数天然友好；但 10 与 95？σ(10)/10 = 9/5，σ(95)/95 = 24/19——不同，故 10 目前是「孤独数」候选（已知最小的孤独数集合包含 1..5）。
How to use the Friendly Number Calculator
- Fill in the inputs with your own numbers — every field shows what it expects.
- The result updates instantly as you type; no "Calculate" click needed.
- Read the result card for the main figure, the step-by-step formula, and practical notes.
Frequently asked questions
Is the Friendly Number Calculator free?
Yes — all math calculators on Calcton are free, with no sign-up required. Your inputs are processed in your browser and never sent to a server.
Is there a Chinese version of this tool?
Yes. Use the Chinese version link above — it is the same calculator with the interface in Simplified Chinese.
References
Formulas and benchmarks used by this calculator follow these published sources.
KevinContent LeadCalcton Editorial Team · Last updated 2026-09-25
Kevin maintains Calcton's formula verification and content: every calculator cites the standard it implements, worked examples are recomputed programmatically, and health benchmarks follow WHO and international guidelines.
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About math calculators
Free online math calculators for algebra, statistics, number theory and everyday arithmetic — from quadratic equations and matrices to percentages, fractions and prime factorization, each with step-by-step formulas.