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 A228126 Sum of prime divisors of n (with repetition) is one less than the sum of prime divisors (with repetition) of n+1. 8
 2, 3, 4, 9, 20, 24, 98, 170, 1104, 1274, 2079, 2255, 3438, 4233, 4345, 4716, 5368, 7105, 7625, 10620, 13350, 13775, 14905, 20220, 21385, 23408, 25592, 26123, 28518, 30457, 34945, 35167, 38180, 45548, 49230, 51911, 52206, 53456, 56563, 61456, 65429, 66585 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS This is an extension to Ruth-Aaron pairs. Sum of prime factors (inclusive of multiplicity) of pair of Consecutive positive integers are also consecutive. The number of pairs less than 10^k (k=1,2,3,4,5,6,..) with this property are 4,7,8,19,55,149,... Up to 10^13 there are only 5 sets of consecutive terms, namely, (2, 3), (3,4), (27574665988, 27574665989), (862179264458, 1862179264459) and (9600314395008, 9600314395009). - Giovanni Resta, Dec 24 2013 The sum of reciprocals of this sequence is approximately equal to 1.3077. - Abhiram R Devesh, Jun 14 2014 LINKS Harvey P. Dale, Table of n, a(n) for n = 1..300 Giovanni Resta, eRAPs: the 446139 terms < 10^12 Carlos Rivera, Extension to Ruth Aaron pairs EXAMPLE For n=20: prime factors = 2,2,5; sum of prime factors = 9. For n+1=21: prime factors = 3,7; sum of prime factors = 10. MATHEMATICA spd[n_]:=Total[Flatten[Table[#[], #[]]&/@FactorInteger[n]]]; Rest[ Position[ Partition[Array[spd, 70000], 2, 1], _?(#[]-#[]==1&), {1}, Heads->False]//Flatten] (* Harvey P. Dale, Sep 07 2016 *) PROG (Python) ## sumdivisors(n) is a function that would return the sum of prime ## divisors of n. i=2 while i < 100000: ..sdi=sumdivisors(i) ..sdip=sumdivisors(i+1) ..if sdi==sdip-1: ....print i, i+1 ..i=i+1 (PARI) sopfm(n)=my(f=factor(n)); sum(i=1, #f[, 1], f[i, 1]*f[i, 2]) for(n=1, 10^5, if(sopfm(n)==sopfm(n+1)-1, print1(n, ", "))) /* Ralf Stephan, Aug 12 2013 */ CROSSREFS Cf. A001414, A006145 Ruth-Aaron numbers (1): sum of prime divisors of n = sum of prime divisors of n+1. Sequence in context: A243902 A086865 A258274 * A352197 A192988 A280016 Adjacent sequences: A228123 A228124 A228125 * A228127 A228128 A228129 KEYWORD easy,nonn AUTHOR Abhiram R Devesh, Aug 11 2013 EXTENSIONS More terms from Ralf Stephan, Aug 12 2013 STATUS approved

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Last modified February 6 20:00 EST 2023. Contains 360111 sequences. (Running on oeis4.)