The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A272779 Numbers n such that  n*(n+1)/2 - sigma(n) = concat(s,t) and  n = s + t, where sigma(n) is the sum of the divisors of n. 1
 10, 15, 24, 136, 196, 1266, 5217, 8236, 8695, 46338, 98826, 181000, 387145, 705250, 1226175, 1291122, 3809269, 8778718, 9294985, 37478179, 49945002, 63158635, 159342696, 175624512, 419753094, 4606837030, 4939169059, 10229566834 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS EXAMPLE 10*11/2 - sigma(10) = 55 - 18 = 37 and 3 + 7 = 10; 5217*5218/2 - sigma(5217) = 13611153 - 7296 = 13603857 and 1360 + 3857 = 5217. MAPLE with(numtheory): P:=proc(q) local a, b, c, i, n; for n from 1 to q do c:=n*(n+1)/2-sigma(n); for i from 1 to ilog10(c) do a:=trunc(c/10^i);  b:=c-a*10^i; if a+b=n then print(n); break; fi; od; od; end: P(10^9); MATHEMATICA Select[Range[10^5], Function[n, Total@ Boole@ Function[k, n == First@ # + Last@ # & /@ Map[FromDigits /@ TakeDrop[IntegerDigits@ k, #] &, Range[IntegerLength@ k - 1]]][n (n + 1)/2 - DivisorSigma[1, n]] > 0]] (* Michael De Vlieger, May 07 2016, Version 10.2 *) ok[t_, n_] := Catch@ Block[{p=10}, While[p

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 29 06:29 EDT 2020. Contains 337425 sequences. (Running on oeis4.)